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Page:Popular Science Monthly Volume 19.djvu/172

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THE POPULAR SCIENCE MONTHLY.

trum hygrometricum, a kind of fungus which grows underground, the outer envelope—which is hard, tough, and hygrometric—divides, when mature, in strips from the crown to the base; these strips spread horizontally, raising the plant above its former position in the ground; on rain or damp weather supervening the strips return to their former

PSM V19 D172 Vallisneria spiralis.jpg
Fig. 1.—Valisneria spiralis. a, female flower; b, male flower; c, floating pollen.

position; on the return of the drought this process is repeated, until the fungus reaches the surface and spreads out there; then the membrane of the conceptacle opens and emits the spores in the form of dust.

I have already referred to the case of the common dandelion. Here the flower-stalk stands more or less upright while the flower is expanded, a period which generally lasts for three or four days. It then lowers itself, and lies more or less horizontally and concealed during the time the seeds are maturing, which in our summers occupies about twelve days. It then again rises, and, becoming almost erect, facilitates the dispersion of the seeds, or, speaking botanically, the fruits, by the wind. Some plants, as we shall see, even sow their seeds in the ground, but these cases will be referred to later on.