DJV. n 



GYMNOSPERMAE 



591 



and chlorophyll is wanting. Towards the base two to eight macrosporangia are 

 borne on the margins, in the place of pinnae. It is evident that each female plant 

 of Cycas which has reached the flowering condition 

 exhibits a regular succession of flowering and vegeta- 

 tive periods. The flower represented by the group 

 of sporophylls is always grown through by the further 

 development of the apex which does not branch. 

 The male plant of Cycas and the other Cycadaceae 

 bear their sporophylls in terminal cones often of 



FIG. 582o. Macros porophyll 

 (Carpel) of Cycas revoluta. 



FIG. 5826. Microsporophyll (stamen) of Cycas circinalis. 



great size, while the further growth of the plant is effected by a lateral bud 

 which continues the direction of growth of the sympodial axis, displacing the 

 cone to one side. 



The cones consist of numerous sporophylls arranged spirally on the axis. The 

 microsporophylls bear large numbers of micro- 

 sporangia on the lower surface (Fig. 5826). 



The macrosporophylls of the cone-bearing Cyca- /a /I 



daceae are considerably modified as compared 

 with Cycas, and each bears two marginal macro- 

 sporangia (Fig. 583). For the developmental 

 history cf. p. 562. 



Order 2. Ginkgoinae 



The single representative of the Family of 

 the Ginkgoaceae which forms this order is 

 Ginkgo biloba. This tree comes from Japan, but 

 is often seen in cultivation in Europe. The 

 long -stalked leaves are divided dichotoniously 

 into two or more lobes and are shed annually. 

 The flowers are dioecious. The numerous stamens FIG 5S3 ._ Cernto:amia robusta . Macro . 

 are situated on an elongated axis which bears sporophy 11 with two macrosporangia. 

 no enveloping leaves. Microsporaugia with an (After GOEBEL.) 

 " endothecium " (cf. p. 546). Macrosporangia in 



pairs at the summit of short shoots ; sporophylls reduced to a collar-like out- 

 growth around the base of the sporangium (Fig. 584). Developmental history, 

 cf. p. 562. 



