Open main menu

Page:Popular Science Monthly Volume 19.djvu/176

This page has been validated.
164
THE POPULAR SCIENCE MONTHLY.

the sweet violet attempted to shoot its seeds, the capsules not being sufficiently elevated, the seeds would merely strike against some neighboring leaf, and immediately fall to the ground. Hence, I think, we see that the arrangement of the capsule in each species is that most suitable to the general habit of the plant.

In the true geraniums again, as for instance in the herb-robert (Fig. 6), after the flower has faded, the central axis gradually elongates (Fig. 6, c, d). The seeds, five in number, are situated at the base of the column, each being inclosed in a capsule, which terminates upward in a rod-like portion, which at first forms part of the central axis, but gradually detaches itself. When the seeds are ripe the ovary raises itself into an upright position (Fig. 6, e); the outer layers of the rod-like termination of the seed-capsule come to be in a state of great tension, and eventually detach the rod with a jerk, and thus throw the seed some little distance. Fig. 6, f, represents the central rod after the seeds have been thrown. In some species, as for instance in Geranium dissectum, Fig. 7, the capsule-rod remains attached to the central column, and the seed only is ejected.

It will, however, be remembered that the capsule is, as already observed, a leaf folded on itself, with the edges inward, and in fact in the geranium the seed-chamber opens on its inner side. You

PSM V19 D176 Geranium dissectum.jpg
Diagram. Fig. 7.—Geranium dissectum. a, just before throwing seed; b, just after throwing seed; c, the capsule still attached to the rod; d, the seed.

will, therefore, naturally observe to me that, when the carpel bursts outward, the only effect would be that the seed would be forced against the outer wall of the carpel, and that it would not be ejected, because the opening is not on the outer but on the inner side. Your remark is perfectly just, but the difficulty has been foreseen by our