322 



THE CYCADALES 



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

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

 these bundles, but the principal increase is effected by the for- 

 mation of new bundles outside of those first formed. Concentric 

 bundles also occur in the leaves and portions of the stem of 

 certain species. The foliage leaves are large and leathery and 

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

 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 

 sporangia are borne on more or less modified leaves arranged 

 in large terminal strobili and either scattered over the sporophyll 

 or sometimes arranged in groups suggestive of the sori of the 

 ferns, in some forms even showing a rudimentary annulus. In 



FlG. 244. Zamia, a cycad common in southern Florida, with strohilus of 

 megasporophvlls. — H. O. Hanson. 



origin and development, they are strikingly like the lower ferns. 

 There is a considerable variation in the form of the sporophylls 

 and the distribution of the sporangia. For example, in Cycas, 

 the megasporophvlls are loosely associated and only slightly 



