248 GINEG0ACEJ3. 



cells, so far as we know at present, are always non-motile ; but, 

 on the other hand, spermatozoids similar to those of Ginltgo have 

 recently been discovered in two genera of Cyoads, Cyeas ' and 

 Zmnio,? The fertilization of the egg-cell by means of spermatozoids 

 affords an important distinction between the Ginkgoales and 

 Coniferse, and serves as another connecting link between Ginkgo 

 and the Cycads. There are several features, as regards both 

 vegetative and reproductive characters, in which Ginkgo shows 

 a distinct approach to the recent Cycads ; and the Cyoadaceee are 

 linked to the Ferns by several Palaeozoic genera of plants, which 

 it is now customary to include in the class Cyoadofllioes. In 

 the Ginkgoacese, then, we have a family connected by several 

 characters with the Cycadacese, and, like the Cycads, exhibiting 

 certain points of contact with the Eems. 



Ginkgo is the sole surviving representative of the Ginkgoales, 

 but there is good reason for including in the same class certain fossil 

 genera characteristic of the Mesozoic epoch. In the first place 

 we have several fossil species usually referred to Ginkgo itself ; 

 the genus Baiera is another closely allied type which should be 

 placed in the same family, and I believe we may reasonably 

 include in the Ginkgoacese the type of female flower to which 

 Carruthers gave the name Beania? There are several other 

 genera which are often referred to the same family with Ginkgo, 

 both of Palseozoio and Mesozoic age, but these need not be 

 discussed here. The only other genus, represented in the Inferior 

 Oolite strata of East Yorkshire, which need be considered as a 

 possible claimant for membership of the Ginkgoacese is Heer's 

 C%ekanowskia, in which is now included the plant named by 

 Lindley & Hutton Solenites Murrayana ; for reasons stated else- 

 where I have considered Czekanowskia as a Conifer of which the 

 precise position is a matter of uncertainty. The evidence on which 

 a close relationship of Heer's genus with Ginkgo has frequently 

 been assumed to exist, is not strong enough to justify any 

 statement which would imply more than a possibility of the two 

 genera belonging to the same family. 



1 Ikeno (98). 



2 AVebber'(97). 



^ Camithei'9 (67). 



