DEVELOPMENT OF PLANTS 417 



with each other, so that the flower has three planes of symmetry. 

 At maturity the walls of the ovary become papery and split 

 down the side, thus freeing the seeds. This form of fruit is 

 known as the capsule, and is of very common occurrence in the 

 order (Fig. 287, C). The development of a conspicuous perianth 

 is a noteworthy departure. It protects the microspores and 

 therefore replaces the bracts and spathe of preceding orders, 

 but owing to its peculiar coloration and form, it also serves as 

 an attraction to special kinds of insects. In the preceding 

 forms that attracted insects, the inducements were usually 

 in the nature of shelter and food, which was largely the micro- 

 spores that were offered freely to all. Such flowers are princi- 

 pally visited by a low order of stupid flies and beetles that are 

 rather promiscuous feeders and are quite as likely to go from 

 a flower of one species to that of a different kind, or to some 

 other object and so defeat the principal object of the flower. 

 With the development of the perianth, however, the flower is 

 equipped with a device that primarily serves to exclude these less 

 desirable visitors and to attract the more intelligent ones. In 

 Erythronium the perianth is in a horizontal position, so that it 

 offers a natural landing place for the insect, and the inducement 

 is a sugary solution secreted by nectar glands concealed at the 

 base of the perianth. It is an easy task for the more intelligent 

 long-tongued insects, like the bees, wasps and butterflies, to reach 

 the nectar in this type of flower. Such insects come to know by 

 experience how to gather the food from a particular form of 

 flower and consequently they will often confine their attention to 

 a single species during their entire flight; consequently the flower 

 by excluding the less intelligent and slothful insects is more cer- 

 tain of being properly crossed. The development of nectar and 

 also of odor glands is among the important variations that 

 appear in the evolution of the flower. It is chiefly by means of 

 the perfumes derived from these organs that the insect is directed 

 to the flowers. The coloration is also of service, when the insect 

 is near to the flower, thus supplementing the perfume glands by 

 directing him to the proper entrance. Some of the larger and 



more brightly colored members of this and other orders appa- 



27 



