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Thus, if the spirals be 8 and 5, (as in Fig. 30,) then each of the 8 will be found to have taken one complete turn before it reaches the apex, and if the numbers be 13 and 8, the 13 will be found to have twisted themselves once round the axis. This seems to be the rule followed by the set of spirals containing the larger number. The other set appears also to have a rule. In cones with the ordinary relation between the height and width, that is, where the circumference is greater than the height, the number of turns made by the set of spirals of the lower number is 2, that is, the spirals go twice round the axis before reaching the apex. But in cones whose height is great in proportion to their width, whose length is greater than their circumference, as, for example, Pinus Strobus, Pinaster, excelsa, monticola, Lambertiana, filifolia, and Abies alba, excelsa, Douglasii, the number of turns taken by the spirals is 3.

Such co-ordinated facts as these may possess little interest to the mere technical naturalist, whose sole aim is to discover new genera and species, or the mere practical horticulturist or arboriculturist, whose object is to find plants of commercial value. But they tend to raise up profound reflections in the truly philosophical mind, and open up glimpses to the religious mind of the deep things of God. They shew that the plant, and all its members, had been before the mind of God prior to the time when He said, "Let the earth bring forth grass, the herb yielding seed, and the fruit-tree yielding fruit after his kind, whose seed is in itself upon the earth, and it was so ;" "and God saw that it was good." Mathematical figures, more or less modified to suit special ends, make their appearance everywhere among the members of the plant. The mathematical spiral regulates the arrangement of all the appendages of the plant.

Even the lines which man has not been able to express in mathematical formulæ, such as the curve of the veins and branches, and the outline of the coma of a tree, are evidently regulated by models in the mind of the Divine Architect. Numerical relations of a most interesting character cast up among every class of plants, and among all the organs of every plant. All appendicular organs, whether belonging to the nutritive or reproductive system, are homotypes. Nay, correspondences may be detected between the disposition and the distribution of branches and leaf veins, sufficient to entitle us to represent root, stem, and leaf, as homotypes, and to prove that there is a unity of composition in the structure of the whole plant.

SECT. II. TRACES OF SPECIAL ADAPTATION IN THE ORGANS OF THE PLANT.

Our aim in this chapter is to shew that in the structure of the plant there are combined simplicity of general plan and variety of modification, the latter for special ends. Having endeavoured in the preceding section to demonstrate the first great truth, we are in this section to illustrate the second.

It is evident that stem and common leaves would not suffice to fit the plant for the discharge of all its functions. It needs, among others, organs or appendages for covering, for support, and for enabling it to propagate and perpetuate itself. To meet these wants members are found to spring up at the very place where they are needed, and at the very time when they are needed; and when they appear they come not as absolutely new organs, but after the old type, modified to serve the present purpose. Does the plant demand a covering ?—

the leaf becomes a scale, or the cuticle produces hairs for that purpose. Is defence required against external attack?-leaves or branches become sharpened or hardened at the point, and the whole plant, or the more assailable parts of it, are bristled all over with spines or prickles. That the species may live on in a new individual, the leaf takes a yet greater departure from its type, and becomes a stamen or pistil. The general plan of the Great Architect is kept up, and yet every several member fulfils a purpose. We cannot conceive of stronger or more convincing evidence of design being supplied to human intelligence.

1. ORGANS OF VEGETATION.

The general structure of the leaf has been already described; we are now to contemplate some well-marked special modifications. The cuticle, or skin, shews numerous small openings, (the stomata of botanists;) these, like the holes in a barn, keep up the communication between the air and the interior. In the leaves of aerial plants, which have the usual horizontal position, these pores are commonly abundant upon the lower surface, and upon that under surface the skin is also of a more delicate nature; on the upper surface the stomata are usually less numerous, or even, in some cases, wanting, while the skin is tougher and denser. In leaves, again, which float on the surface of the water, the openings are confined to the upper surface, and in submerged leaves they are wanting altogether. The intervening portion of the leaf, already described, called parenchyma, presents some remarkable peculiarities in relation to the pores we have been describing. Next the upper surface of the leaf, it consists of compact oblong cells, placed perpendicularly and in close contact with each other, the

layer nearest the lower surface is less dense, and numerous vacant spaces occur between the cells, permitting free communication, through the stomata or pores, between

FIG. 31.*

the atmosphere and

the interior of the
leaf. We have here,
therefore, a striking
example of harmony
between the struc-
ture of this part of
the plant and its
function and
and po-
sition. The pores
are exhaling and
absorbing organs;
where they are most

[graphic]

abundant, there we find loose texture of the parenchyma, permitting free communication; where stomata are not needed, they are wanting; when they are required on a particular part of the leaf, there we find them. Many species of Utricularia-delicate water-plants-have numerous small sacs connected with the leaves, which are stated, about the flowering period, to become filled with air, and to buoy the plant near the surface of the water. In Pontederia crassipes and Trapa natans, some of the leaves have the stalk dilated into an air cavity, which acts as a float. The magnificent Victoria Regia presents several interesting features. It is an aquatic belonging to the water-lily family, and the fully developed leaf reaches a diameter of five feet or more. In order to give strength to such a large surface, the veins on the lower aspect of the leaf are of great depth, acting as so many

FIG. 81. Perpendicular section of leaf, to shew different structures of upper and lower portions.

supporting girders. Between them are formed spaces in which air might accumulate and lead to a rupture of the parts; such an occurrence, however, is obviated by the perforations which constitute one of the pecularities of this remarkable plant. By transmitted light the leaf resembles a sieve, with numerous minute openings.

Stipules. These appendages assume different forms, and vary in size and texture, according to the plant in which we examine them. They are, as already stated, formed after the leaf type, and although we cannot, in every case, point out the purposes served by their modified form, there are, nevertheless, instances in which we cannot doubt that they are present for a useful object. In Lathyrus aphaca they are of large size, and supply the place of the leaves, which are absent in the mature plant. In not a few plants they perform important functions as protecting organs, forming a covering to the young leaves; this is obvious enough in Magnolia, in the Indian-rubber fig, and in the submerged Potamogetons. When the leaves expand, these protective stipules fall off; their function being performed they are no longer needed, and so they disappear.

Covering of plants.-The varied aspect of the external surface of the different organs of plants, so important to the botanist in the distinction of species, and designated by the terms downy, silky, scaly, &c., is owing to the presence of certain minute appendages, the nature of which has been already described. (See p. 86.) In certain cases their presence has some relation to the habitat or dwelling-place of the plant. Those on the upper part of the pistil of hare-bell are well-known to act in collecting and retaining the pollen grains as they drop from the anther. There can be no doubt that in many cases the very minute fibrils on the underground parts

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