| FIG. 43.—Cone of jack-pine closely covering its seeds, often for several years. | FIG. 44.—Cone of jack-pine as opened by heat, sowing seeds. |
CHAPTER VI.
PLANTS THAT SHOOT OFF THEIR SPORES OR SEEDS.
By numerous devices a large number of the lower plants send off their ripe spores with considerable force. Some call them sling fruits. One in particular, Pilobolus cristallinus, found about damp stables, I have observed to shoot black masses of spores to a spot on a wall six feet above the ground, with enough force to have carried them not less than twelve feet. When ripe and dry, the spores of most ferns are shot from the parent plant by a motion forcible enough not only to burst the sporangium, the vessel that contains the spores, but also to turn it inside out.
| FIG. 45.—Spores of Pilobolus before and while shooting its spores. |
35. Dry pods twist as they split open and throw the seeds.—In December, while absent from home, I collected for future study some pods of the Chinese wistaria, and left them on my desk in the library for the night. The house was heated by a hot-air furnace. In the morning the pods were in great confusion; most of them had split and curled up, and the seeds were scattered all about the room. As usual the little daughter, an only child, was accused of spoiling my specimens, but she showed her innocence. A little investigation and a few experiments with some pods not yet opened explained the whole matter satisfactorily. The stout pods grow and ripen in a highly strained condition, with a strong tendency to burst spirally, the two half-pods being ready to coil and spring in opposite directions; when the valves can no longer hold together, they snap with a sharp noise and sling the heavy seeds, giving them a good send-off into the world. As a pair of birds build a nest, hatch eggs, rear their young, and then send them forth to seek their fortunes, so for months the mother plant had labored, had produced and matured seeds, which at last it scattered broadcast. Goethe, Kerner von Marilaun, each independently, and very likely others, had an experience with ripe pods brought to a warm room very similar to my own. In many cases the ripe and drying fruits are "touched off" by wind jostling the branches or by animals passing among them; in the latter case there is a chance that a portion of the discharges will be lodged somewhere on the animal and be carried along with it.
36. A seed case that tears itself from its moorings.—The perennial phlox in cultivation distributes its seeds in the following manner: when ripe, the calyx becomes dry and paper-like, and spreads out in the form of a saucer. The thick-walled dry pistil opens from the top into three pieces with a snap, spreading open so far against the calyx that it is torn from the brittle attachment; away go the seeds, mingled with the fragments of the pistil, no longer of any use.
| FIG. 46.—A dry pod of wild bean bursting spirally to throw the seeds. |