THE EVIDENCE 71 



the Cycads effect their fertilisation by means of 

 actively moving male cells, the spermatozoids. 



This important discovery was first made in 

 the genus Cycas, by one of the Japanese observers 

 just mentioned, and was immediately afterwards 

 extended to Zamia by Webber's researches; sper- 

 matozoids have since been demonstrated in Stan- 

 geria, Ceratozamia, Microcycas and Dioon, and 

 are no doubt common to the whole family. It 

 may be added that the very first Seed-plant in 

 which spermatozoids were found was not a Cycad, 

 but the Maidenhair- tree (Ginkgo), where they 

 were observed by Hirase a month or two before 

 their discovery in Cycas by Ikeno. A short ac- 

 count of the process as it has been observed in 

 Cycas and Zamia may be given before we further 

 consider the significance of the facts. 



The ovule, at the time when it is ready to re- 

 ceive the pollen, is about the size of a grain of 

 Maize, or a small Hazel-nut. It consists of an 

 outer envelope and a central body, the two being 

 closely united except at the top, where a narrow 

 passage (the micropyle) is left open in the envel- 

 ope, leading down to the central body, or nucellus, 

 as it is technically called (fig. 7, D). The apex of 

 the nucellus becomes excavated to form a deep pit, 

 the pollen-chamber, a character ony shown by the 

 Cycads and the Maidenhair-tree among living 

 plants, though common in Palaeozoic seeds (see 

 Chapter IV). 



