CHAPTER IX 



POLLINATION AND FERTILIZATION 



Review. — It has been stated that the essential female element of 

 reproduction in the flower is produced in the nucellus of the ovule, the 

 male by the germination of the pollen-grain. It has also been shown 

 that these two elements are produced separately, and in most cases 

 remotely, from one another, and that some means must exist for bring- 

 ing them together in order that fertilization may be effected. 



POLLINATION 



In those plants (Gymnosperms, Figs. 174 and 175) in which no 

 stigma exists, this is accomplished by immediate contact of the pollen 

 with the ovule, which is exposed for the purpose. In those in which a 

 stigma exists, it is accomplished by the deposit and fixation of the 

 pollen thereupon. To either of these processes the term Pollination 

 is applied. 



Close-pollination and Cross-pollination. — The two elements may 

 proceed from the same flower, in which case the term Self-pollination or 

 Close-pollination is applied, or they may proceed from different flowers, 

 in which case the term Cross-pollination is applied. It will be noted 

 further that there are degrees of cross-pollination, according to whether 

 the elements proceed from flowers upon the same or upon dift'erent 

 plants. When the flowers are perfect, it is at least possible in most 

 cases for them to be either close- or cross-pollinated. 



Cross-pollination Beneficial. — In nearly all cases, the reproductive 

 function is strengthened through cross-pollination, which explains 

 the fact that nearly all flowers are constructed so as to facilitate the 

 process, while most of them are so constructed as to incommode, and 

 very many to prevent, close-pollination. In a few cases the flower is 

 constructed so as to prevent cross-pollination. 



Methods of Securing Cross-pollination. — The methods of efl'ecting 

 cross-pollination may be divided into the ordinary and the exceptional. 



