132 



THE EVOLUTION OF SEX. 



who strongly opposed it, and denied the sexuality of plants altogether. 

 In 1830, however, Amici made a great step. He traced the pollen 

 grain from its lighting on the carpel tip down into the recesses of the 

 ovule. Schleiden, whose name is so closely associated with the 

 founding of the "cell theory," soon confirmed Amici's observation, 

 but in doing so went unfortunately much too far. Not only did the 

 pollen-grain send its tube into the ovule, but there, according to 

 Schleiden, it gave origin to the future embryo. This opinion, which, 

 as Heyer observes, made the male element realiy female, was obviously 

 parallel to that of the zoologists who found in the "sperm-animalcule" 

 the miniature embryo. The view of Camerarius and Amici of course 

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



—e 



n 



FlG. 42. — A, Enlarged section of ripe Anther (b), liberating pollen (a). B, Diagrammatic 

 section of a Flower, showing female parts (c), — receiving stigma, conducting style, 

 ovary with seed (d); the male parts, stamens {6) with pollen. C, The Pollen-tube (a) 

 growing down to the ovule (<■/) and female cell (e). The pollen grain is here represented 

 as distinctly two-celled, cf. pp. 131 and 212. 



is a male element which unites in fertilization with a female cell, but, 

 thanks especially to Strasburger, much about the intimate nature of 

 the process. In the last century Millington emphasized 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 fertilization essentially involves the union of the nuclei of 

 male and female cells. By analogy the same was belived to be true 

 of higher plants, but direct demonstration has only recently been 

 forthcoming. Strasburger has followed 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 gen- 

 erative cell, of which only the latter is directly important in fertiliza- 



