158 



ELEMENTARY STUDIES IN BOTANY 



flowers. A flower that has an indefinite number of members, 

 and that is polypetalous, hypogynous, and regular, has a 

 combination of characters that puts it low in the scale of 

 Angiosperms. On the other hand, a flower with a definite 

 number of members, and that is sympetalous, epigynous, 



and irregular, has a com- 

 bination of characters that 

 ranks it very high. By 

 observing the combina- 

 tions in the flower, the 

 relative positions of the 

 flowering plants may be 

 estimated. 



99. Pollination by in- 

 sects. It has been stated 

 ( 86, p. 143) that the pre- 

 vailing method of pollina- 

 tion among Angiosperms 

 is the use of insects as the 

 agents of transfer. The 

 method of transfer by 

 means of the wind, as 



FIG. 127. Longitudinal section of an iris /~i j 



flower, showing a stamen between the among UymnOSpermS and 

 drooping petal and the petal-like style ; 



the stigmatic shelf is seen at the top of the 

 style above the stamen; the nectar pit is 

 at the junction of petal and stamen; 

 observe the section of the ovary, whose 

 position shows that the flower is epigy- 

 nous. After GRAY. 



many Angiosperms, is 

 wasteful, in the sense that 

 there must be a great 

 amount of pollen pro- 

 duced in order that a little 



of it may be sure to reach the right spots. When insects 

 carry pollen directly from one plant to another, pollination 

 becomes so definite a process that a comparatively small 

 amount of pollen is sufficient to insure pollination. 



The transfer of pollen from the stamen to the pistil of the 

 same flower is called self-pollination, while transfer to the 

 pistil of another flower is called cross-pollination. The 



