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A TEXTBOOK OF THEORETICAL BOTANY 



Microcycas. This genus has the most primitive gametophytes in the 

 order. The pollen grains form sixteen or more antherozoids, and the female 

 prothallus produces as many as two hundred archegonia. There is only one 

 species, M. calocoma, confined to Cuba. 



Zamia. Comparatively small plants with the stems usually underground 

 and tuberous. They occur in tropical America from Florida to Chile. 



Macrozamia. Large and not infrequently branched. The cones are 

 the largest in the order and are sometimes truly lateral. The heavy seeds 

 are forcibly ejected to a distance of several yards. M. moorei, in Queensland, 

 is poisonous to stock and is eradicated by injecting with arsenic. The genus 

 is confined to Australia. 



Fig. 709. — Encephalartos horridiis photo- 

 graphed in Kew Gardens. 



Ceratozamia. The ovulate sporophylls have two spines which give the 

 plant its name. The genus occurs in southern Mexico. 



Dioon. Comparatively dwarf plants. The ovulate sporophylls have 

 long overlapping points. The genus occurs in southern Mexico. 



Stangeria. The only genus with network venation in the leaves, which 

 are remarkably fern-like. The genus occurs in South-east Africa. 



Encephalartos. The ovulate sporophylls are shield-shaped, somewhat 

 like those oi Zamia, and do not overlap as in Dioon. The name arises from 

 the fact that one species yields an edible pith from the crown of the stem. 

 The genus occurs in South Africa (Fig. 709). 



Bozvema. The leaves are bipinnate and spreading. The genus occurs in 

 Queensland (Fig. 710). 



