SECT. II 



PHANEROGAMIA 



')29 



Cycas is a native of Asia ; Macrozamia and Bowenia of Australia. Enccphal- 

 artos and Stangcria are African, while America has the genera Dioon, Ccratozamia, 

 Zamia, and Microcycas. 



The stem, which undergoes secondary growth in thickness, is as a rule 

 unbranched and bears large, pinnate foliage leaves. These, which are of 



firm leathery texture and persist for a number 

 of years, alternate with smaller scale-leaves and 

 form a large terminal crown. The surface of 

 the cylindrical or tuberous stem is clothed with 

 the scale-leaves and the bases of the old foliage 

 leaves. Mucilage ducts are present in all parts 

 of the plant. The vascular bundles are collateral 

 but their xylem consists of tracheides only. 



Fio. 4'.tS. — Carpel of Cycas re- 

 voluta. (After Sachs, re- 

 duced.) 



Fig. 499.— Stamen of Cycas circinalis, from below. (After Richard.) 



The Cycadaceae are dioecious. Fig. 497 represents a female plant 

 of Cycas revoluta, in which the growing point forms alternate zones 

 of foliage leaves and macrosporophylls. 

 When young the foliage leaves are rolled 

 up circinately as in the Ferns. One of 

 the sporophylls is represented in detail in 

 Fig. 498. It shows the pinnate form of 

 the foliage leaf, but is densely covered 

 with hairs, and chlorophyll is wanting. 

 Towai'ds the base two to eight macro- 

 sporangia are borne on the margins. It 

 is evident that each female plant of 

 Cijcas which has reached the flowering 

 condition exhibits a regular succession of 

 flowering and vegetative periods. The 

 floAver 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 of the other Cycadaceat bear their sporophylls in terminal cones 

 often of great size, while the further growth of the plant is effected 



2 M 



Fio. 500. — Ceratozumia robusta. Macro- 

 sporophyll with two macrosporangia. 

 (After GoEBEi,.) 



