Fig. 459.
Proterogyny in skunk’s cabbage.
(Photograph by the author.)
Fig. 460.
Skunk’s cabbage;
upper flowers
proterandrous,
lower ones
proterogynous.
852. Now if we observe the spadix of another plant we may see a condition of things similar to that shown in [fig. 460]. In the flowers in the upper part of the spadix here the anthers are wedging their way through between the armor-like plates formed by the sepals, while the styles of the same flowers are still beneath, and the stigmas are not ready for pollination. Such flowers are proterandrous, that is, the anthers are ripe before the stigmas of the same flowers are ready for pollination. In this spadix the upper flowers are proterandrous, while the lower ones are proterogynous, so that it might happen here that the lower flowers would be pollinated by the pollen falling on them from the stamens of the upper flowers. This would be cross pollination so far as the flowers are concerned, but not so far as the plants are concerned. In some individuals, however, we find all the flowers proterandrous.
853. Spiders have discovered this curious relation of the flowers and insects.—On several different occasions, while studying the adaptations of the flowers of the skunk’s cabbage for cross pollination, I was interested to find that the spiders long ago had discovered something of the kind, for they spread their nets here to catch the unwary but useful insects. I have not seen the net spread over the opening in the spathe, but it is spread over the spadix within, reaching from tip to tip of either the stigmas, or stamens, or both. Behind the spadix crouches the spider-trapper. The insect crawls over the edge of the spadix, and plunges unsuspectingly into the dimly lighted chamber below, where it becomes entangled in the meshes of the net.
Flowers in which the ripening of the anthers and maturing of the stigmas occur at different times are also said to be dichogamous.
854. Pollination of jack-in-the-pulpit.—The jack-in-the-pulpit (Arisæma triphyllum) has made greater advance in the art of enforcing cross pollination. The larger number of plants here are, as we have found, diœcious, the staminate flowers being on the spadix of one plant, while the pistillate flowers are on the spadix of another. In a few plants, however, we find both female and male flowers on the same spadix.
855. The pretty bell-flower (Campanula rotundifolia) is dichogamous and proterandrous ([fig. 462]). Many of the composites are also dichogamous.
856. Pollination of orchids.—But some of the most marvellous adaptations for cross pollination by insects are found in the orchids, or members of the orchis family. The larger number of the members of this family grow in the tropics. Many of these in the forests are supported in lofty trees where they are brought near the sunlight, and such are called “epiphytes.” A number of species of orchids are distributed in temperate regions.