354 



THE CYCADS 



decidedly palm-like in appearance, with stems 12 to 60 feet high. 

 The vascular bundles are collateral and arranged around a large 

 pith as noted in BotrycJiium. A slight enlargement of the stem 

 is brought about owing to the weak growth of the cambium of 

 these bundles, but in some genera the principal increase is effected 

 by the formation of new bundles outside of those first formed. 

 Fern types of bundles also occur in the leaves, cortex and strobili 

 of certain species. The foliage leaves are large and leathery and 

 form a rosette, alternating with scale leaves, at the apex of the 



Fig. 244, Zamia, a cycad common in southern Florida, with strobilus of 

 megasporophylls. — H. O. Hanson. 



Stem. The bases of these leaves form an armor-like plate over 

 the surface of the stems. In certain genera, the young leaves 

 are coiled as in the ferns. 



(a) The Sporophylls and Sporangia of the Cycads. — The spor- 

 angia are borne on more or less modified leaves arranged in 

 large strobili at the top of the stem, though rarely on the apex. 

 Unlike preceding cases these strobili are of two kinds, the one 

 bearing only megasporangia, the other microsporangia. Further- 

 more these two kinds of strobili are on different plants. The 

 sporangia are either scattered over the sporophyll or arranged in 



