SEXUAL REPRODUCTION. 



141 



ature embryo. The view of Camerarius and Amici of course 

 prevailed ; and we now know not only the fact that the pollen- 

 grain is a male element which unites in fertilisation with a 

 female cell, but, thanks especially to Strasburger, much about the 

 intimate nature of the process. In the last century, Millington 

 emphasised the difference between male and female flowers, 

 and we can trace the influence of this discovery in Erasmus 

 Darwin's " Loves of the Plants." 



In the last few decennia, it has been shown, for many of the 

 lower plants, that fertilisation essentially involves the union of 

 the nuclei of male and female cells. By analogy the same was 

 believed to be true of higher plants, but direct demonstration 

 has only recently been forthcoming 



Strasburger has followed 



Illustrating the contrast between male and femal flowers in the pink 

 campion {Lychnis diurna). 



the whole history of the pollen-grain, from the anther of the 

 stamen to the embryo-sac of the carpel ; and though some details 

 still remain obscure, his researches have undoubtedly succeeded 

 in elucidating the essential facts in the process. He shows 

 how the pollen-grain divides into a vegetative and generative 

 cell, of which only the latter is directly important in fertilisation. 

 The generative cell, which consists like the sperm mostly 

 of nucleus with very little directly associated cell-substance, 

 itself divides to form two (or even more) generative nuclei. 

 One of these passes from the pollen-tube to enter into close 

 union with the nucleus of the female cell, with which it fuses 

 to form the double nucleus ruling the forthcoming develop- 

 ment. Exceptionally the other generative nucleus may also 



