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attacked by it within the hop-garden. If the infected leaves are left to rot they carry on the parasitic fungus to

a new season.

It

An interesting fact has been discovered about the hopblight aphis (called by zoologists Phorodon humuli). It appears that the winter brood of this little insect (when the hop-vine has died down) deposit their eggs on the bark of the sloe (the wild plum), and also that any cultivated plum trees serve them for the same purpose. When the hop is dead they must of necessity get nourishment and shelter from the plum tree. Clearly, then, if you can keep all plum trees at a distance of half a mile from your hopgarden you will render it very difficult, if not impossible, for the blight aphis to carry on from season to season. will rarely, if ever, travel half a mile, and not in any number. But hop-growers have not always the control of the cultivation for half a mile around their hop-fields, though large growers should be able to acquire it. The skilful grower even finds it useful to leave one or two plum trees in the hop-field, so as to attract the winter brood of the blight aphis to them, and then he falls upon the devastating but minute rascals with quassia and other poisons, and ensures their destruction. The increase of plum orchards in the neighbourhood of hop-gardens is probably a chief cause of the increased loss by hop-blight of late years in Kent.

The hop-louse has other enemies besides the grower. These are the lady-birds (less prettily called "lady-bugs"), which feed greedily on the parasites, so that when the hop-grower sees plenty of them on a hop-vine he does not trouble to wash it. And there are other predaceous insects which tend to keep the hop-lice down. Cultivation and excessive production have resulted in putting, as it were, too heavy a task upon the natural enemies of the pest, whilst the more delicate but valuable varieties of

hop cannot withstand the attacks of blight, which less valuable varieties would tolerate without fatal injury.

Another complicated and difficult problem for the hop-grower is the "curing" of the hops when gathered. He has to arrange to grow a number of varieties which will not be all ready for picking at the same moment, so that the hop-pickers may be employed for some six weeks, and gather each kind at the exact time of ripeness. Then the gathered hops have to be "dried" and "cured." In Germany (where the highest-priced hops are produced) small cultivators dry them in the sun, and they are "cured" by the purchaser, but in England they are dried in kilns (called "oasts" in Kent) near the hop-grounds. They are cured with sulphur fumes on the spot as soon as dried. The object of the drying and curing is quickly to get rid of the water, which forms 75 per cent. of the weight of the green flower-heads, but is reduced by drying to 10 per cent., and to destroy the "mould" (fungus) which may be present, and to keep the hops free from new access of mould by the slight deposit of sulphur fumes on their surface. The drying and fumigating require a great deal of skill, and a fine crop may be injured or even rendered worthless by want of care, rapidity, and judgment in treating the freshly gathered flower-cones. It is said that it takes years to acquire the art, and that skilled hop-curers are more difficult to obtain than formerly.

The natural difficulties and fluctuations with which the English hop-grower has to contend are made far more serious by the fact that he does not know what will be the yield of the American and German hop-plantations, and so cannot prepare beforehand for the demands of the market. It appears that ice-storage is now being made use of in some districts to hold over any excess of produce of particular kinds of hop beyond the special demand for those

kinds. But a formidable source of trouble exists (and, it appears, must always exist) in the enormous changes and expansion of the brewing industry in all parts of the globe. It is actually the case that there has been a greatly increased and unforeseen demand for hops of less highly developed aroma, for the purpose of brewing light ales with little of the perfume given by the finest and hitherto most highly priced hops. So that, having expended skill and money to produce the finest hops, and having been favoured by the weather, a grower may find that his pains have been thrown away, and that there is a sudden falling-off in the demand for the beautiful highpriced crop which he has gathered in. There is no remedy for these world-wide fluctuations in the market, and the only way in which the grower can protect himself is by combining with others to procure information from every part of the world as to the probable production and the probable demand of the various qualities of hops a year or more in advance of his planting. More has been done in America and in Germany in this way than in England, and it is probable that the future success or failure of hop-growing in this country depends more on the possibility of obtaining correct information in regard to the tendencies of production in all hop-growing countries, and in regard to the demand in all the brewing industries of the world, than on anything else.

This brief sketch of the hop-growing industry is sufficient to show what a very difficult problem is before those who desire to take legislative measures for the preservation of the old industry of the hop-garden in this country. But it must not be at once assumed, because the case is a difficult and complicated one, that nothing can be done, and that the beautiful hop-vines and the finest hops are necessarily to be banished from the English soil.

THE

XXXV

GREEN-FLIES, PLANT-LICE, AND

PARTHENOGENESIS

HE minute "green-flies" which attack all kinds of plants, and among which are ranked the hoplouse or hop-blight, the rose aphis or green-fly of rose trees, the woolly blight or aphis of apple trees and pear trees, and the terrible vine-killer-the Phylloxera vastatrix -form a special group of bug-like insects known as the Aphides. They have soft cylindrical bodies, six legs, sometimes two pairs of transparent wings, sometimes none, and a sharp beak (in some kinds this is one and a half times as long as the body), with which they prick the soft parts of plants, when they suck up the juices which issue from the wound (Fig. 59). There is in the temperate regions of the world a special kind of aphis or plant-louse peculiar to each of many kinds of flowering plants, including most trees. A very complete, illustrated account of the kinds or species of British aphides, amounting to some two hundred, was produced by the late Mr. Buckton, F.R.S., and published by the Ray Society.

There are many facts of extraordinary interest about these tiny swarming insects. In the first place, they are closely related to the minute scale-insects or Coccida, several species of which produce the celebrated lac of lacquer-work and the dyes known as lake, cochineal, and

kermes, the latter a dye manufactured in South Europe and used to colour wool and cloth crimson before cochineal reached us from Mexico. The Coccida include also the "mussel-scale" and other destructive diseases of fruit trees. A beautiful purple colour can be extracted from crushed masses of some kinds of aphides (as well as from Coccida), and has been used as a dye. The aphides have very generally a green colour, like many insects (caterpillars and leaf insects) which pass their lives upon green leaves and feed on them. It is often supposed that this green colour is merely the green colouring matter (so-called chlorophyll) of the leaf, taken up by the insects in feeding on the leaf. But this is not so; it is a peculiar substance derived in a crude state from the plant-juice, but digested in the stomach and completed in the insects'

FIG. 59.-Side view of winged viviparous female of the hop-louse. 6, the stabbing beak.

FIG. 58.-Foundress or stock-mother of the hoplouse: the individual hatched from a winter egg, laid on the bark of a plum tree, who produces viviparously a wingless virgin brood. That brood produces wing-bearing young, which fly off to the hopplants.

blood and tissues.
Then, again, the aphides
produce curious secre-
tions, often in great
abundance, which sur-
round them as the lac
surrounds the lac-insect.
The threads which are
produced in
in such
abundance, by the
woolly aphis of apple

trees, as to look like masses of cotton wool adhering to the twigs of the tree, are of this nature.

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