Page:Popular Science Monthly Volume 19.djvu/174

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162
THE POPULAR SCIENCE MONTHLY.

When the seeds are fully ripe, the capsule opens by three valves and allows them to escape.

In the dog-violet (Viola canina, Fig. 3) the case is very different. The capsules are less fleshy, and, though pendent when young, at

PSM V19 D174 Viola canina.jpg
Fig. 3.—Viola canina. a, bud; b, bud more advanced; c, capsule open, some of the seeds are already thrown.

maturity they erect themselves (Fig. 3, c), stand up boldly above the rest of the plant, and open by the three equal valves (Fig. 4) resembling an inverted tripod. Each valve contains a row of three, four, or five brown, smooth, pear-shaped seeds, slightly flattened at the upper,

PSM V19 D174 Viola canina seed vessel before and after ejection of seeds.jpg
 Fig. 4.  Fig. 5. Viola canina; seed-vessel
 after ejecting the seeds.

wider end. Now the two walls of each valve, as they become drier^ contract, and thus approach one another, thus tending to squeeze out the seeds. These resist some time, but at length the attachment of