. Popular science monthly. es, andfrom this point of view they are of a more normal character, the prin-cipal difference, indeed, being in size. The grass pea (X. nissolia. Fig. 32) is also a small species. It livesin meadows and the grassy borders of fields, and has lost altogether,not only the leaves, but also the tendrils. Instead, however, of en-larged stipules, the functions of the leaves are assumed by the leaf-stalks, which ax*e elongated, flattened, linear, ending in a fine point,and, in fact, so like the leaves of the grasses among which the plantlives that it is almost impossible to
. Popular science monthly. es, andfrom this point of view they are of a more normal character, the prin-cipal difference, indeed, being in size. The grass pea (X. nissolia. Fig. 32) is also a small species. It livesin meadows and the grassy borders of fields, and has lost altogether,not only the leaves, but also the tendrils. Instead, however, of en-larged stipules, the functions of the leaves are assumed by the leaf-stalks, which ax*e elongated, flattened, linear, ending in a fine point,and, in fact, so like the leaves of the grasses among which the plantlives that it is almost impossible to distinguish it except when inflower. For a weak plant growing among close grass, a long linearleaf is, perhaps, physically an advantage ; but one may venture to sug-gest that the leaves would be more likely to be picked out and eatenif they were more easily distinguishable, and that from this point ofview also the similarity of the plant to the grass among which it growsmay also be an advantage. THE POPULAR SCIENCE MONTHLY. Fia. 32. In looking at foliage I have often been much puzzled as to whythe leaves of some species are tongue-shaped, while others are , for instance, the black bryony (Tamus communis) and the com-mon biyony {Bryonia dioica). Again, why are the veins in some leaves pinnate, like those of the beech andelm, and others palmate, as in the mapleand sycamore ? My first idea was that this might havereference to the arrangement of the woodyfibers in the leaf-stalk. If we make a sec-tion of the stalk of a leaf, we shall find thatin some cases the woody fibers are collectedin the middle, while in others there are sev-eral distinct bundles, separated by cellularparenchyma. My first idea was that eachof the primary ribs of a leaf might repre-sent a separate woody fiber in the leaf-stalk, so that leaves with a single bundleof woody fibers would be pinnate; thosewith several distinct bundles, palmate. The first species which I examined fa-vored this view. The mel
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1872
