44 2 RELATION TO ENVIRONMENT. 



for pollination before the anthers of the same flower are ripe, are proter- 

 ogynous. 



852. Now if we observe the spadix of another plant we may see a condi- 

 tion 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 pol- 

 lination 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 proter- 

 androus. 



853 Spiders have discovered this carious relation of the flowers and in- 

 sects. 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 tney 

 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 (Arisaema 

 triphyllum) has made greater advance in the art of enforcing cross pollina- 

 tion. The larger number of plants here are, as we have found, dioecious, 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 bellflower (Campanula rotundifolia) is dichogamous 

 and proterandrous (fig. 462). Many of the composites are also dichoga- 

 mous. 



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. 



