94 POLLINATION AND FERTILIZATION 



responsible for some of the most far-reaching economic conditions and 

 results in the history of the drug trade. In exceptional instances, still 

 other animals take part in this work. 



Participation by other Parts than the Flower. — It may be remarked in 

 passing that these characters, like some of those which follow, are not 

 restricted to the flower itself. Very frequently other portions of the 

 plant adjacent to the flower will be expanded, brightly colored, and 

 developed into special forms, while the odor of some flowers, due to 

 the presence of glandular tissues, is shared by the foliage and other 

 herbaceous portions, as in the lavender. Well-formed, large glands are 

 present in the axils of the primary veins of the leaves of some species 

 of Cinchona, although the precise function which they perform is by 

 no means clearly established. 



Provisions for Utilizing Insect- visits. — The special contrivances for 

 utilizing insect-visits in effecting pollination are far more elaborate 

 and varied than those for inducing them, which we have already 

 considered, and our consideration of them cannot be extended beyond 

 what is necessary to indicate their general nature and classification, 

 and to serve as a key in understanding the complicated modifications 

 which we have observed the typical flower to undergo. Usually the 

 effects extend in two directions — (a) toward excluding the pollen from 

 access to the stigma of its own flower, and (6) toward securing its 

 access to that of another. 



Dichogamy. — One of the most frequent methods of securing the 

 former result is the maturing of the androecium and gynaecium at 

 different times. This method is called Dichogamy. 



Proterogyny and Proterandry. — By it the ovules of a flower are already 

 fertilized before the mature pollen of that flower escapes from its thecae 

 (Proterogyny), or else the pollen is matured and utilized before the 

 stigmas of that flower are prepared for its reception (Proterandry). 



Proterandry is well illustrated by Figs. 269 and 270. The former 

 illustrates the anthers erect with their pollen ready for removal, while 

 the stigmas are yet immature. The visit of an insect to such a flower 

 cannot affect the stigma, but wiU result in the transportation of the 

 pollen to another flower, perhaps in the condition represented bj^ Fig. 

 270. Here it will be received upon an active stigma, the anthers having 

 already perished and dropped beneath the margin of the corolla. 



Figs. 271 and 272 illustrate proterandry assisted by a special mechan- 

 ical device. The former represents a flower with closely syngenesious 

 and introrsely dehiscent anthers. 



