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Saprolegnia, Achlya, Pylhiopsis, Dictyuchus, A planes. Motile zoospores | a yeast, and even bring about alcoholic fermentation în a saccharine which escape from the zoosporangium are present except in A planes. solution. The sexual reproduction shows all transitions between forms which are normally sexual, like the Peronosporaceae, to forms in which no antheridium is developed and the oospheres develop parthenogenetically. The oogonia, unlike the Peronosporaceae, contain more than one oosphere. Klebs has shown that the development of zoosporangia or of oogonia and pollinodia respectively in Saprolegnia is dependent on the external conditions; so long as a continued stream of suitable food-material is ensured the mycelium grows on without forming reproductive organs, but directly the supplies of nitrogenous and carbonaceous food fall below a certain degree of concentration sporangia are developed. Further reduction of the supplies of food effects the formation of oogonia. This explains the sequence of events in the case of a Saprolegnia-mycelium radiating from a dead fly in water. Those parts nearest the fly and best supplied develop barren hyphae only; in a zone at the periphery, where the products of putrefaction dissolved in the water form a dilute but easily accessible supply, the zoosporangia are developed in abundance; oogonia, however, are only formed in the depths of this radiating mycelium, where the supplies of available food materials are least abundant.

Chytridineae. These parasitic and minute, chiefly aquatic, forms may be looked upon as degenerate Oomycetes, since a sexual process and feeble unicellular mycelium occur in some; or they may be regarded as series of primitive forms leading up to higher members. There is no means of deciding the question. They are usually included in Oomycetes, but their simple structure, minute size, usually uniciliate zoospores, and their negative characters would justify their retention as a separate group. It contains less than 200 species, chiefly parasitic on or in algae and other water-plants or animals, of various kinds, or in other fungi, seedlings, pollen and higher plants. They are often devoid of hyphae, or put forth fine protoplasmic filaments into the cells of their hosts. After absorbing the cell-contents of the latter, which it does in a few hours or days, the fungus puts out a sporangium, the contents of which break up into numerous minute swarm-spores, usually one-ciliate, rarely two-ciliate. Any one of these soon comes to rest on a host cell, and either pierces it and empties its contents into its cavity, where the further development occurs (Olpidium), or merely sends in delicate protoplasmic filaments (Rhizophydium) or a short hyphal tube of, at most, two or three cells, which acts as a haustorium, the further development taking place outside the cell-wall of the host (Chytridium). In some cases resting spores are formed inside the host (Chytridium), and give rise to zoosporangia on germination. In a few species a sexual process is described, consisting in the conjugation of similar cells (Zygochytrium) or the union of two dissimilar ones (Polyphagus). In the development of distinct antheridial and oogonial cells the allied Ancylistineae show close alliances to Pythium and the Oomycetes. On the other hand, the uniciliate zoospores of Polyphagus have slightly amoeboid movements, and in this and the pseudopodium-like nature of the protoplasmic processes, such forms suggest resemblances to the Myxomycetes. Opinions differ as to whether the Chytridineae are degraded or primitive forms, and the group still needs critical revision. Many new forms will doubtless be discovered, as they are rarely collected on account of their minuteness. Some forms cause damping off of seedlings-e.g. Olpidium Brassicae; others discoloured spots and even tumour-like swellings-e.g. Synchylium Scabiosae, S. Succisae, Urophlyctis, &c., on higher plants. Analogies have been pointed out between Chytridiaceae and unicellular algae, such as Chlorosphaeraceae, Protococcaceae, "Palmellaceae," &c., some of which are parasitic, and suggestions may be entertained as to possible origin from such algae.

The Zygomycetes, of which about 200 species are described, are especially important from a theoretical standpoint, since they furnished the series whence Brefeld derived the vast majority of the fungi. They are characterized especially by the zygospores, but the asexual organs (sporangia) exhibit interesting series of changes, beginning with the typical sporangium of Mucor containing numerous endospores, passing to cases where, as in Thamnidium, these are accompanied with more numerous small sporangia (sporangioles) containing few spores, and thence to Chaetocladium and Piptocephalis, where the sporangioles form but one spore and fall and germinate as a whole; that is to say, the monosporous sporangium has become a conidium, and Brefeld regarded these and similar series of changes as explaining the relation of ascus to conidium in higher fungi. According to his view, the ascus is in effect the sporangium with several spores, the conidium the sporangiole with but one spore, and that not loose but fused with the sporangiole wall. On this basis, with other interesting morphological comparisons, Brefeld erected his hypothesis, now untenable, that the Ascomycetes and Basidiomycetes diverge from the Zygomycetes, the former having particularly specialized the ascus (sporangial) mode of reproduction, the latter having specialized the conidial (indehiscent one-spored sporangiole) mode. In addition to sporangia and the conidial spores referred to, some Mucorini show a peculiar mode of vegetative reproduction by means of gemmae or chlamydospores.e. short segments of the hyphae become stored with fatty reserves and act as spores. The gemmae formed on submerged Mucors may bud like

The segments of the hyphae in this group usually contain several nuclei. At the time of sporangial formation the protoplasm with numerous nuclei streams into the swollen end of the sporangiophore and there becomes cut off by a cell-wall to form the sporangium. The protoplasm then becomes cut up by a series of clefts into a number of smaller and smaller pieces which are unicellular in Pilobolus, multicellular in Sporodinia. These then become surrounded by a cell-wall and form the spores. This mode of sporeformation is totally different from that in the ascus; hence one of the difficulties of the acceptance of Brefeld's view of the homology of ascus and sporangium. The cytology of zygospore-formation is not known in detail; the so-called gametes which fuse are multinucleate and are no doubt of the nature of gametangia. The fate of these nuclei is doubtful, probably they fuse in pairs (fig. 6).

Blakeslee has lately made some very important observations of the Zygomycetes. It is well known that while in some forms, e.g. Spordinia, zygospores are easily obtained, in others, e.g. most species of Mucor, they are very erratic in their appearance. This has now been explained by Blakeslee, who finds that the Mucorinae can be divided into two groups, termed homothallic and heterothallic respectively. In the first group zygospores can arise by the union of branches from the same mycelium and so can be produced by the growth from a single spore; this group includes Spordinia grandis, Spinellus permission of Gustav Fischer. fusiger, some species of FIG. 6.- Mucor Mucedo. Different Mucor, &c. The majority of forms, however, fall stages in the formation and germination of the zygospore. (After Brefeld, into the heterothallic group, in which the asso-, 1-4. 5 from v. Tavel, Pilze.) ciation of branches from two mycelia different in I, nature is necessary for the 2, formation of zygospores. These structures cannot 3, then be produced from the product of a single spore nor even from the thalli derived from any two spores. The two kinds of 4. thalli Blakeslee considers to have a differentiation 5,

of the nature of sex and

From Strasburger's Lehrbuch der Botanik, by

Two conjugating branches in contact.
Septation of the conjugating cells (a)
from the suspensors (b).
More advanced stage, the conjugat-
ing cells (a) are still distinct from
one another; the warty thickenings
of their walls have commenced to
form.

Ripe zygospore (b) between the sus-
pensors (a).

Germinating zygospore with a germtube bearing a sporangium. he distinguishes them as (+) and (-) forms; the former being usually distinguished by a somewhat greater luxuriance of growth. The classification of the Mucorini depends on the prevalence and characters of the conidia, and of the sporangia and zygospores-e.g. the presence or absence of a columella in the former, the formation of an investment round the latter. Most genera are saprophytes, but some-Chaetocladium, Piptocephalis are parasites on other Mucorini, and one or two are associated casually with the rotting of tomatoes and other fruits, bulbs, &c., the fleshy parts of which are rapidly destroyed if once the hyphae gain entrance. Even more important is the question of mycosis in man and other animals, referred to species of Mucor, and investigated by Lucet and Costantin. Klebs has concluded that transpiration is the important factor in determining the formation of sporangia, while zygote development depends on totally different conditions; these results have been called in question by Falck.

The Entomophthoraceae contain three genera, Empusa, Entomophthora and Basidiobolus. The two first genera consist of forms which are parasitic on insects. Empusa Muscae causes the wellknown epidemic in house-flies during the autumn; the dead, affected flies are often found attached to the window surrounded by a white halo of conidia. B. ranarum is found in the alimentary canal of the frog and growing on its excrement. In these three genera the conidia are cast off with a jerk somewhat in the same way as the sporangium of Pilobolus.

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B. HIGHER FUNGI. Now that Brefeld's view of the origin | 32 and 64, &c.; in a few cases the number of spores is less than of these forms from the Zygomycetes has been overthrown, eight by abortion of some of the eight nuclei. The ascus is thus one the relationship of the higher and lower forms of fungi is left of the most sharply characterized structures among the fungi. In some forms we find definite male and female sexual organs in obscurity. The term Eumycetes is sometimes applied to this (Sphaerotheca, Pyronema, &c.), in others the antheridium is abortive group to distinguish them from the Phycomycetes, but as the or absent, but the ascogonium (oogonium) is still present and the same name is also applied to the fungi as a whole to differentiate female nuclei fuse in pairs (Lachnea ebore ad ilgge deal stercorea, Humaria granulata, Asco-ds bons mains them from the Mycetozoa and Bacteria, the term had best be bolus furfuraceus); while in other dropped. The Higher Fungi fall into three groups: the Usti- forms ascogonium and antheridium laginales, of doubtful position, and the two very sharply marked are both absent and fusion occurs groups Basidiales and Ascomycetes. between vegetative nuclei (Humaria) rutilans, and probably the majority of other forms). In other cases the sexual fusion is apparently absent altogether, as in Exoascus. In the first case (fig. 9) we have a true sexual process, while in the second and third cases we have a reduced sexual process in which the fusion of other nuclei has replaced the fusion of the normal male and female nuclei. It is to be noted that all the forms exhibit the fusion of nuclei in the ascus, so that those with the normal or reduced sexual process described above have two nuclear fusions in their lifehistory. The advantage or significance of the second (ascus) fusion is not clearly understood.

From Strasburger's Lehrbuch der

Botanik, by permission of Gustav
Fischer.

FIG. 8.-Development of the
Ascus.

A-C, Pyronema

I. Ustilaginales. This includes two families Ustilaginaceae (smuts) and Tilletiaceae (bunts). The bunts and smuts which damage our grain and fodder plants comprise about 400 species of internal parasites, found in all countries on herbaceous plants, and especially on Monocotyledons. They are remarkable for their dark spores developed in gall-like excrescences on the leaves, stems, &c., or in the fruits of the host. The discovery of the yeast-conidia of these fungi, and their thorough investigation by Brefeld, have thrown new lights on the group, as also have the results elucidating the nature of the ordinary dark spores--smuts, bunt, &c.-which by their mode of origin and development are chlamydospores. When the latter germinate a slender" promycelium is put out; in Ustilago and its allies this is transversely septate, and bears lateral conidia (sporidia); in Tilletia and its allies non-septate, and bears a terminal tuft of conidia (sporidia) (fig. 7). Brefeld regarded the promycelium as a kind of basidium, bearing lateral or terminal og ban conidia (comparable to basidioEn spores), but since the number of basidiospores is not fixed, and the basidium has not yet assumed very definite morphological characters, Brefeld termed the group Hemibasidii, and regarded them as a halfway stage in the evolution of the true Basidiomycetes from Phycomycetes, the Tilletia type leading 7500 obyd to the true basidium (Autobasidium), ibalsti rechthe Ustilago type to the protopman dena basidium, with lateral spores; but this 5d1pmantinot view is based on very poor evidence, bitats so that it is best to place these forms include Exoascus, Taphrina, Ascorticium and Endomyces. The Exoascaceae are a small group of doubtful extent here used to plamo as a separate group, the Ustilaginales, okolo ddtom od n The yeast-conidia, which bud off has no 1210g tool box from the conidia or their resulting he sa itsmycelium when sown in nutrient boquita From Vine's Students' Text Book of solutions, are developed in succes-t Botany, by permission of Swan Sonnen sive crops by budding exactly as

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confluens. The group of the Hemiasci was as (After Harper.) founded by Brefeld to include forms D, Young ascus of Bouwhich were supposed to be a connect- do diera with eight spores, ing link between Phycomycetes and (After Claussen.) Ascomycetes. As mentioned before, to bas sai the connexion between these two groups is very doubtful, and the derivation of the ascus from an ordinary sporangium of the Zygomycetes cannot be accepted. The majority of the forms which were formerly included in this group have been shown to be either true Phycomycetes (like Ascoidea) or true Ascomycetes (like Thelebolus). Eremascus and Dipodascus, which are often placed among the Hemiasci, possibly do not belong to the Ascomycetes series at all.

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From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.
FIG. 9.-Sphaerotheca Castagnei. Fertilization and Development
of the Perithecium. (After Harper.)
Oogonium (og) with the an- Fertilized oogonium sur-
theridial branch (az) applied rounded by two layers of
to its surface.
hyphae derived from the
stalk-cell (st).

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Passage of the antheridial or derived by division from the The multicellular ascogonium nucleus towards that of the oogonium; the terminal cell bom 510 Sticay with the two nuclei (as) Union of the nuclei.yd i gives rise to the ascus.no lov ont ai ello lil-sdqed,botsgeolo

4, H. Ascomycetes. This, except in the case of a few of the simpler forms, is a very sharply marked group characterized by a special mycelium is very much reduced in extent. The asci are borne type of sporangium, the ascus. In the development of the ascus we directly on the mycelium and are therefore fully exposed, being find two nuclei at the base which fuse together to form the single devoid from the beginning of any investment. The Taphrineae, nucleus of the young ascus. The single nucleus divides by three which include Exoascus and Taphrina, are important parasitessuccessive divisions to form eight nuclei lying free in the protoplasme.g. pocket-plums and witches' brooms on birches, &c., are due to of the ascus. Then by a special method, described first by Harper, their action (fig. 10). Exoascus and Ascorticium present interesting a mass of protoplasm is cut out round each nucleus; thus eight parallels to Exobasidium and Corticium among the Basidiomycetes. aninucleate ascospores are formed by free-cell formation. The Saccharomycetaceae include the well-known yeasts which belong protoplasm remaining over is termed epiplasm and often contains mainly to the genus Saccharomyces. They are characterized by glycogen (fig. 8). In some cases nuclear division is carried further their unicellular nature, their power of rapid budding, their capacity before spore-formation occurs, and the number of spores is then 16, for fermenting various sugars, and their power of forming endogenous

spores.

cut

-ep

m

as

From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.

The sporangium with its endogenous spores has been compared with an ascus, and on these grounds the group is placed among the Ascomycetes-a very doubtful association. The group has attained an importance of late even beyond that to which it was brought by Pasteur's researches on alcoholic fermentation, chiefly owing to the exact results of the investigations of Hansen, who first applied the methods of pure cultures to the study of these organisms, and showed that many of the inconsistencies hitherto existing in the literature were due to the coexistence in the cultures of several species or races of yeasts morphologically almost indistinguishable, but physiologically very different. About fifty species of Saccharomyces are described more or less completely, but since many of these cannot be distinguished by the microscope, and some have been found to develop physiological races or varieties under special conditions of growth, the limits are still far too ill-defined for complete botanical treatment of the genus. A typical yeast is able to develop new cells by budding when submerged in a saccharine solution, and to ferment the sugar-i.e. so to break up its molecules that, apart from small quantities used FIG. 10.-Taphrina Pruni. for its own substance, masses of Transverse section through the it out of all proportion to the epidermis of an infected plum. mass of yeast used become Four ripe asci, a1, a2, with eight resolved into other bodies, such spores, da, d, with yeast-like as carbon dioxide and alcohol, conidia abstricted from the spores. the process requiring little or no oxygen. Brefeld regards the budding process as the formation of conidia. Under other conditions, of which the temperature is an important one, the nucleus in the yeast-cell divides, and each daughter-nucleus again, and four spores are formed in the mother cell, a process obviously comparable to the typical development of ascospores in an ascus. Under yet other conditions the quiescent yeast-cells floating on the surface of the fermented liquor grow out into elongated sausage-shaped or cylindrical cells and branching cell-series, which mat together into mycelium-like veils. At the bottom of the fermented liquor the cells often obtain fatty contents and thick walls, and behave as resting cells (chlamydospores). The characters employed by experts for determining a species of yeast are the sum of its peculiaritics as regards form and size: the shapes, colours, consistency, &c., of the colonies grown on certain definite media; the optimum temperature for spore-formation, and for the development of the veils "; and the behaviour as regards the various sugars. The following summary of some of the principal characteristics of half-a-dozen species will serve to show how such peculiarities can be utilized for systematic purposes:

After Sadebeck.

st, Stalk-cells of the asci. Filaments of the mycelium cut transversely.

m,

cut, Cuticle. ep, Epidermis.

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and others have shown that a ferment (zymase) can be extracted from yeast-cells which causes sugar to break into carbon dioxide and alcohol. It has since been shown by Buchner and Albert that yeast-cells which have been killed by alcohol and ether, or with acetone, still retain the enzyme. Such material is far more active than the zymase obtained originally by Buchner from the expressed juice of yeast-cells. Thus alcoholic fermentation is brought into line with the other fermentations.

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Schizosaccharomyces includes a few species in which the cells do not "bud but become elongated and then divide transversely. In the formation of sporangia two cells fuse together by means of outgrowths, in a manner very similar to that of Spirogyra; sometimes, however, the wall between two cells merely breaks down. The fused cell becomes a sporangium, and in it eight spores are developed. In certain cases single cells develop parthenogenetically, without fusion, cach cell producing, however, only four spores. In Zygosaccharomyces described by Barker (1901) we have a form of the usual sprouting type, but here again there is a fusion of two cells to form a sporangium.

Cytology. The study of the nucleus of yeast-cells is rendered difficult by the presence of other deeply staining granules termed by Guillermond metachromatic granules. These have often been mistaken for nuclei and have to be carefully distinguished by differential stains. In the process of budding the nucleus divides apparently by a process of direct division. In the formation of spores the nucleus of the cell divides, the protoplasm collects round the nuclei to form the spores by free-cell formation; the protoplasm (epiplasm) not used in this process becomes disorganized. A fusion of nuclei was originally described by Jansens and Leblanc, but it was observed neither by Wager nor Guillermond and is probably absent. In Schizosaccharomyces and Zygosaccharomyces, however, we have a fusion of nuclei in connexion with the conjugation of cells which precedes sporangium-formation. The theory may be put forward that the ordinary forms have been derived from sexual forms like Schizosaccharomyces and Zygosaccharomyces by a loss of sexuality, the sporangium being formed parthenogenetically without any nuclear fusion. This suggests a possible relationship to Eremascus, which can only doubtfully be placed in the Ascomycetes (vide supra). Carpoascomycetes.-The other divisions of the Ascomycetes may be distinguished as Carpoascomycetes because they do not bear the asci free on the mycelium but enclosed in definite fruit bodies or ascocarps. The ascocarps can be distinguished into two portions, a mass of sterile or vegetative hyphae forming the main mass of the fruit body, and surrounding the fertile ascogenous hyphae which bear at their ends the asci. When the ascogonium (female organ) is present the ascogenous hyphae arise from it, with or without its previous fusion with an antheridium. In other cases the ascogenous hyphae arise directly from the vegetative hyphae. In connexion with this condition of reduction a fusion of nuclei has been observed in Humaria rutilans and is probably of frequent occurrence. The asci may be derived from the terminal cell of the branches of the ascogenous hyphae, but usually they are derived from the penultimate cell, the tip curving over to form the so-called crozier. By this means the ascus cell is brought uppermost, and after the fusion of the two nuclei it develops enormously and produces the ascospores. The ascospores escape from the asci in various ways, sometimes by a special ejaculation-mechanism. The Ascomycetes, at least the Carpoascomycetes, exhibit a well-marked alternation of sexual and asexual generations. The ordinary mycelium is the gametophyte since it bears the ascogonia and antheridia when present; Characters of Sugars Fermented and Cells. Products, &c.

Spores.

Veils.

Fermentation.

Spores.

30°

20°-28°

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S. Pastorianus I.

27°-5°

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S. ellipsoideus

25

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Two questions of great theoretical importance have been raised over and over again in connexion with yeasts, namely, (1) the morphological one as to whether yeasts are merely degraded forms of higher fungi, as would seem implied by their tendency to form elongated, hypha-like cells in the veils, and their development of ascospores as well as by the wide occurrence of yeast-like sprouting forms" in other fungi (e.g. Mucor, Exoasci, Ustilagineae, higher Ascomycetes and Basidiomycetes); and (2) the question as to the physiological nature and meaning of fermentation. With regard to the first question no satisfactory proof has as yet been given that Saccharomycetes are derivable by culture from any higher form, the recent statements to that effect not having been confirmed. At the same time there are strong grounds for insisting on the resemblances between Endomyces, a hyphal fungus bearing yeast-like asci, and such a form as Saccharomyces anomalus. Concerning the second question, the recent investigations of Buchner

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ascogenous hyphae with their asci represent the sporophyte since they are derived from the fertilized ascogonium. The matter is complicated by the apogamous transition from gametophyte to sporophyte in the absence of the ascogonium; also by the fact that there are normally two fusions in the life-history as mentioned earlier. If there are two fusions one would expect two reductions, and Harper has suggested that the division of the nuclei into eight in the ascus, instead of into four spores as in most reduction processes, is associated with a double reduction process in the ascus. Miss Fraser in Humaria rutilans finds two reductions: a normal synaptic reduction in the first nuclear division of the ascus, and a peculiar reduction division termed bruckymeiosis in the third ascus division.

Various types of ascocarp are characteristic of the different divisions of the Carpoascomycetes: the cleistothecium, apothecium and perithecium.

Perisporineae. This includes two chief families, Erysiphaceae | characterized in general by the possession of an ascocarp which, and Perisporiaceae. They are characterized by an ascocarp without though usually a completely closed structure during the earlier any opening to the exterior, the ascospores being set free by the stages of development, at maturity opens out to form a bowl or decay or rupture of the ascocarp wall; such a fruit-body is termed saucer-shaped organ, thus completely exposing the layer of asci a cleistothecium (cleistocarp). The Erysiphaceae are a sharply which forms the hymenium. Such an ascocarp goes by the name of marked group of forms which live as parasites. They form a super-apothecium. Owing to the shape of the fruit-body many of these ficial mycelium on the surface of the plant, the hyphae not usually forms are known as cup-fungi, the cup or apothecium often attaining penetrating the tissues but merely sending haustoria into the epi- a large size, sometimes several inches across (fig. 12). Functional dermal cells. Only in rare cases is the mycelium intercellular. male and female organs have been shown to exist in Pyronema and Owing to their appearance they go by the popular name of mildews. Boudiera; in Lachnea stercorea Sphaerotheca Humuli is the well known hop-mildew, Sphaerotheca both ascogonia and antheridia Mors-Uvae is the gooseberry mildew, the recent advent of which are present, but the antheridium has led to special legislation in Great Britain to prevent its spreading, is non-functional, the ascogonial as when rampant it makes the culture of gooseberries impossible. (female) nuclei fusing in pairs; Erysiphe, Uncinula and Phyllactinia are other well-known genera. this is also the case in Humaria The form of the fruit body, the difference and the nature of special granulata and Ascobolus furfur outgrowths upon it-the appendages-are characteristic of the aceus, where the antheridium is various genera. Besides peritheca the members of the Erysiphaceae entirely absent. In H. rutilans, possess conidia borne in simple chains. De Bary brought forward however, both sexual organs are very strong evidence for the origin of the ascocarp in Sphaerotheca absent and the ascogenous and Erysiphe by a sexual process, but Harper in 1895 was the first hyphae arise apogamously from to prove conclusively, by the observation of the nuclear fusion, that the ordinary hyphae of the my there was a definite fertilization in Sphaerotheca Humuli by the celim. In all these cases the e. fusion of a male (antheridial) nucleus with a female, ascogonial (oogonial) nucleus. Since then Harper has shown that the same process occurs in Erysiphe and Phyllactinia.

The Perisporiaceae are saprophytic forms, the two chief genera being Aspergillus and Penicillium. The blue-green mould P. crustaceum and the green mould A. herbariorium (Eurolium herbariorum) are extraordinarily widely distributed, moulds being found on almost any food-material which is exposed to the air. They have characteristic conidiophores bearing numerous conidia, and also cleistothecia which are spherical in form and yellowish in colour. The latter arise from the crown of a spirally coiled archicarp (bearing an ascogonium at its end) and a straight antheridium. Vegetative hyphae then grow up and surround these and enclose them in a continuous sheath of plectenchyma (fig. 11). It has lately been shown by Fraser and Chambers that in Eurolium both

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ascogonium and antheridium contain a number of nuclei (ie. are
coenogametes), but that the antheridium disorganizes without
passing its contents into the ascogonium. There is apparently a
reduced sexual process by the fusion of the ascogonial (female)
nuclei in pairs. Aspergillus Oryzae plays an important part in
saccharifying the starch of rice, maize, &c., by means of the abundant
diastase it secretes, and, in symbiosis with a yeast which ferments
the sugar formed, has long been used by the Japanese for the pre-
paration of the alcoholic liquor saké. The process has now been
successfully introduced into European commerce.
Discomycetes.-Used in its widest sense this includes the
Hysteriaceae, Phacidiaceae, Helvellaceae, &c. The group is

From Strasburger's Lehr buch der Botanik, by permis sion of Gustav Fischer.

FIG. 12.-Peziza aurantiaca. (After Krombholz, nat. size.)

FIG. 13. Ascobolus furfuraceus. Diagrammatic section of the fructification. (After Janczewski.)

m, Mycelium.

c, Archicarp.

1, Pollinodium.

S, Ascogenous filaments.
a, Asci.

r, p, The sterile tissue from which
the paraphyses h spring.

ascogonium and antheridium contain numerous nuclei; they are to be looked upon as gametangia in which there is no differentiation of gametes, and since they act as single gametes they are termed coenogametes. In some forms as in Ascobolus the ascogonium is multicellular, the various cells

communicating by pores in
the transverse walls (fig. 13).

In the Helvellaceae there is
no apothecium but a large
irregular fruit body which at
maturity bears the asci on its
surface. The development is
only slightly known, but there
is some evidence for believing
that the fruit-body is closed in
its very carly stages.

The genus Peziza (in its widest sense) may be taken as the type of the group. Most of them grow on living plants or on dead vegetable remains, very often on fallen wood; a number, however, are found growing on earth which is rich in humus. The genus Sclerotinia may be mentioned here; a number of forms have been investigated by Woronin. The conidia are fragrant and are carried by bees to the stigma of the bilberry; here they germinate with the pollen and

From Strasburger's Lehrbuch der Botanik,

the hyphae pass with the pollen by permission of Gustav Fischer.
tubes down the style; the
former infect the ovules and FIG. 14. Perithecium of Podo-
produce sclerotia, therein re- spora fimiseda in longitudinal section
After v. Tavel.
ducing the fruits to a mum-
mified condition.
From the $, Asci.
sclerotia later the apothecium, Paraphyses.
develops. One species, S., Periphyses..
heteroica, is heteroecious; the m, Mycelial hyphae.
ascospores infecting the leaves of Vaccinium uliginosum, while the
conidia which then arise infect only Ledum palustre. This is the
only case of heteroecism known in the vegetable kingdom outside
the Uredineae.

Pyrenomycetes.-This is an extraordinarily large and varied group of forms which mostly live parasitically or saprophytically on vegetable tissue, but a few are parasitic on insect-larvae. The group

is characterized by a special type of ascocarp, the perithecium. This is typically of a flask-shaped form opening with a small pore at the top. The asci live at the bottom often mixed with paraphyses, while the upper "neck" of the flask is lined with special hyphae, the periphyses, which aid in the ejection of the spores (fig. 14). The simpler forms bear the perithecía directly on the mycelium, but the more highly developed forms often bear them on a special mycelial development-the stroma, which is often of large size and special shape and colour, and of dense consistence. The cytological details of development of the perithecia are not well known; most of them appear to develop their ascogenous hyphae in an apogamous way without any connexion with an ascogonium. Besides the special ascocarps, accessory reproductive organs are known in the majority of cases in the form of conidia.

Tuberineae.-These are a small group of fungi including the wellknown truffles. They are found living saprophytically (in part parasitically) underground in forests. The asci are developed in the large dense fruit bodies (cleistothecia) and the spores escape by the decay of the wall. The fruit-body is of complicated structure, but its early stages of development are not known. Many of the fruit-bodies have a pleasant flavour and are eaten under the name of truffles (Tuber brumale and other species). The exact life-history of the truffle is not known.

Laboulbeniineae are a group of about 150 species of fungi found on insects, especially beetles, and principally known from the researches of Thaxter in America. The plant is a small, dark brown, erect structure (receptacle) of a few cells, and 1-10 mm. high, attached to the insect by the lowermost end (foot), and easily mistaken for a hair or similar appendage of the insect. The receptacle ends above in appendages, each consisting of one or a few cells, some of which are the male organs, others the female organs, and others again may be barren hairs. The male organ (antheridium) consists of a few cells, the terminal one of which either abstricts from its end, or emits from its interior the non-motile spermatia, reminding us of those of the Florideae. The female organ is essentially a flask-shaped structure; the neck of the flask growing out as the trichogyne, and the belly composed of an axial carpogenic cell surrounded by investing cells, and with one cell (trichophoric) between it and the trichogyne. These three elements-trichogyne, trichophoric cell, and carpogenic cell-are regarded as the procarp. The spermatia have been shown by Thaxter to fuse with the trichogyne, after which the axial cell below (carpogenic cell) undergoes divisions, and ultimately forms asci containing ascospores, while cells investing this form a perithecium, the whole structure reminding us essentially of the fructification of a Pyrenomycete. Many modifications in details

د

From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer. FIG. 15.-Armillaria mellea. (After Ruhland.)

A, Young basidium with the two primary nuclei. B. After fusion of the two nuclei. Hypholoma appendiculatum. C. A basidium before the four nucleiderived from the second

ary nucleus of the basidium have passed into the four basidiospores. D, Passage of a nucleus through the sterigma into the basidio

occur, and the plants may be dioecious. No injury is done to the infested insects. It has lately been shown that there is a fusion of nuclei in connexion with ascus formation, so that there can be no doubt of the position of this extraordinary group of plants among the Ascomycetes. The various cells of these organisms are connected by large pits which are traversed by thick protoplasmic threads connecting

one cell with the next. In this point and in their method of fertilization the Laboulbeniineae suggest a possible relationship of Ascomycetes and the Red Algae.

the

Basidiales.-This very large group of plants is characterized by the possession of a special type of conidiophore-the basidium, which gives its name to group. The basidium is a unicellular or multicellular structure from which four basidiospores arise as outgrowths; but soon, like the ascus, becomes it starts asa binucleate structure, uninucleate by the fusion of the two nuclei.. Then two successive nuclear divisions occur resulting in the formation of four nuclei which later migrate respectively into the four basidiospores (fig. 15). The Basidiales are further characterized by the complete loss of normal sexuality, but at some time or other in the life-history there takes place an association of two nuclei in a cell; the two nuclei are derived from separate cells or possibly in some cases are sister nuclei of the same cell. The two nuclei when once associated are termed "conjugate" nuclei, and they always divide at the same time, a half of each passing into each cell. This conjugate condition is finally brought to a close by the nuclear fusion in the basidium. Between the nuclear association and the nuclear fusion in the basidium many thousands of cell generations may be intercalated.

spore.

This nuclear association of equivalent nuclei apparently represents a reduced sexual process (like the fusion of female nuclei in Humaria granulata and of vegetative nuclei in H rutilans, among the Ascomycetes) in which, however, the actual fusion (normally, in a sexual process, occurring immediately after association) is delayed until the formation of the basidium. During the tetrad division in the basidium nuclear reduction occurs. There is thus in all the Basidiales an alternation of generations, obscured, however, by the apogamous transition from the gametophyte to sporophyte. The sporophyte may be considered to begin at the stage of nuclear association and end with the nuclear reduction in the basidium.

Uredineae. This is a large group of about 2000 forms. They are all intercellular parasites living mostly on the leaves of higher plants. Owing to the presence of oily globules of an orange-yellow or rusty-red colour in their hyphae and spores they are termed Rust-Fungi. They are distinguished from the other fungi and the rest of the Basidiales by the great variety of the spores and the great elaboration of the life-history to be found in many cases. Five different kinds of spores may be present-teleutospores, sporidia (=basidiospores), aecidiospores, spermatia and uredospores (fig. 16). The teleutospore, with the sporidia which arise from it, is always present, and the division into genera is based chiefly on

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its characters. The teleutospore puts forth on germination a fourcelled structure, the promycelium or basidium, and this bears later four sporidia or basidiospores, one on each cell. When the sporidia infect a plant the mycelium so produced gives origin to accidiospores and spermatia; the aecidiospores on infection produce a mycelium which bears uredospores and later teleutospores. This is the lifehistory of the most complicated forms, of the so-called eu forms. In the opsis forms the uredospores are absent, the mycelium from the hemi the aecidiospores are absent, the mycelium from the sporidia aecidiospores producing directly the teleutospores. In brachy and giving origin directly to the uredospores; the former possess spermatia, in the latter they are absent. In lepto and micro forms both accidiospores and uredospores are absent, the sporidia producing a mycelium which gives rise directly to teleutospores; in the lepto forms the teleutospores can germinate directly, in the micro forms only after a period of rest. We have thus a series showing a progressive reduction in the complexity of the life-history, the lepto and micro forms having a life-history like that of the Basidiomycetes. The eu and opsis forms may exhibit the remarkable phenomenon of heteroecism, i.e. the dependence of the fungus on two distinct host-plants for the completion of the life-history. Heteroecism is very common in this group and is now known in over one hundred and fifty species. In all cases of heteroecism the sporidia infect one host leading to the production of aecidiospores and spermatia (if present), while the accidiospores are only able to infect another

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