IlfFLrKXCE OF POLLEN UPON THE FBUIT 311 



LX. INFLUENCE OF POLLEN UPON THE 

 FRUIT 



377. We have found (147, 148) that fertihza- 

 tion by pollen is essential to the development of 

 perfect seeds. One pollen grain is sufficient to 

 impregnate an ovule; yet very many grains may 

 fall upon a stigma, and the ovary may contain 

 but a single ovule. The question is raised, there- 

 fore, as to what becomes of the extra or redun- 

 dant pollen. We may suppose (from an analogy 

 with buds) that many of the grains may fail out- 

 right; and this is true. Does the pollen exercise 

 any other function than to impregnate the ovule? 



377a. The body or sti-ucture which is impregnated is, strictly 

 speaking, not the ovule but the egg-cell of the embryo-sac ; but an 

 explanation of the process of fecundation is not intended here. The 

 pollen grain sends out a tube (the process is generally called germi- 

 nation), which penetrates the stigma and style and reaches the 

 embryo-sac, where a sperm cell is discharged. As a rule, one pollen 

 grain fecundates one egg-cell, but the pollen-tube may branch and 

 fecundate more than one egg-cell. There are certain instances in which 

 seeds have been produced without fertilizaliion, but they are exceptions, 

 and do not require discussion here. 



3776. In recent writings the ovule is often denominated the 

 macrosporangium. The pollen grain is called a microspore. These 

 are terms of comparative morphology and physiology, and need not 

 be used here. 



378. We have seen that the pulp of the straw- 

 berry fails to develop at points where the akenes 



