Page:Popular Science Monthly Volume 2.djvu/306

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292
THE POPULAR SCIENCE MONTHLY.

mens of the berberry, etc., and is then directly connected with the process of fertilization of the ovule. In Stylidium, an Australian genus, the style and filaments are adherent into a column, which hangs over on one side of the flower. When touched, it rises up and springs over to the opposite side, at the same time opening its anthers and scattering the pollen. The stamens of the various species of Berberis and Mahonia, to the former of which our common berberry belongs, exhibit this irritability to a remarkable degree. If touched with a pin or other object at the base of the inside face of the filament, the stamen will spring violently forward from its place within the petal, so as to bring

Fig. 8.
PSM V02 D306 Australian stylidium.jpg

the anther into contact with the stigma, as shown in Fig. 8, and will after a time slowly resume its original position. At first sight it may seem as if this contrivance were intended to insure the fertilization of the pistil from the pollen of its own flower. In reality, however, the reverse is the case; the excitation takes place in Nature when an insect entering the flower, for the sake of the honey in the glands at the base of the pistil, touches the inside of one of the stamens. The pollen is thus thrown on to the head or body of the insect, which carries it away to the next flower it visits, and leaves some of it on the stigma, and thus cross-fertilization instead of self-fertilization is secured. Similar motion of the stamens toward the pistil, but spontaneous, takes place in the case of the London Pride, and other species of Saxifraga.

Elasticity is, indeed, a common property of organized tissue, though it is not often developed to so evident an extent. In the "touch-me-not," or Impatiens, we have a familiar instance in the seed-vessel, which, if touched when nearly ripe, suddenly coils back, throwing the seeds to a considerable distance. The "squirting cucumber" (Momordica elaterium) marks the period of ripeness by the fruit separating from its stalk, and expelling the seeds and juice with great violence. Mr. Thomas Meehan described a remarkable instance of elasticity at a recent meeting of the Academy of Natural Sciences of Philadelphia. The seeds—or, as would appear from his description, more correctly the embryos of the seeds—of the American "witch-hazel" (Hamame-