140 



THE EVOLUTION OF SEX. 



along capillary spaces between the leaves, to the passive female 

 cells. In some cases there is a curvature of the male organ 

 towards an adjacent female organ, apparently in obedience to 

 chemical or physical attraction. Even here close fertilisation 

 seems exceptional, and is often impossible. 



So far, however, only the external aspect of the process. 

 As long ago as 1694, Camerarius showed that if the male 

 flowers of hemp, maize, and other plants were removed, the 

 female flowers bore no seeds, or at least no fertile ones. In 

 1704, E. F. Geoff"roy castrated certain plants by removing the 

 stamens, and noted that they remained barren. " Mirandum 

 sane," he wrote, "quam similem servet natura cunctis in 

 viventibus generandis harmoniam." Reasonable as this now 

 appears to us, the fundamental fact was not only slowly recog- 

 nised, but on into the present century there were found 



A, Enlarged section of ripe Anther {/>), liberating pollen (a). J), Diagrammatic 

 section of a Flower, showing female parts (c),— receiving stigma, conduct- 

 ing style, ovar^^ w ith seed (cf) ; the male parts, stamens {/>) with pollen. C, 

 The Pollen-tube (a) glowing down to the ovule (</)and female cell (e). The 

 pollen grain is here represented as distinctly two-celled, cf. pp. 142 and 229. 



naturalists 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 really female, was obviously parallel to that of 

 the zoologists who found in the "sperm-animalcule" the mini- 



