DEVELOPMENT OF PLANTS 339 



pith as noted in Botrychiiim. 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. 



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

 megasporophylls. — H. O. Hanson. 



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

 angia 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 

 origin and development, they are strikingly like the Ophioglos- 

 sales. There is a considerable variation in the form of the sporo- 

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

 Cvcas, the megasporophylls are loosely associated and only 



