PRACTICAL POLLINATION 261 



details of its flowers and fruit. But that the 

 pollen grain actually has these potentialities has 

 been demonstrated thousands of times over by 

 the plant experimenter. 



Any amateur who wishes to test the matter 

 may do so, to his complete satisfaction, by making 

 the simplest experiment in cross-pollenizing and 

 watching the growth of the hybrid seedlings his 

 work brings forth. 



The pollen grain effects union with the ovule 

 by sending out a threadlike filament of proto- 

 plasm, like a tiny root, which penetrates the 

 stigmatic surface, passes down along through the 

 style, and carries the nucleus of the pollen grain 

 to the nucleus of an ovule. When the two 

 nuclei come in contact, fertilization has been 

 accomplished. 



When pistil and the stamens have been con- 

 sidered, we are through with the really essential 

 mechanisms of the flower. 



From the human standpoint, of course, chief 

 interest centers in the corolla with its widespread- 

 ing petals of varied colors. To the plant itself 

 this structure is in a sense essential, inasmuch 

 as it supplies the visible signal that attracts the 

 attention of the insect. But beyond this it has 

 no share in the process of fecundation. We shall 

 have occasion to consider the form and structure 



