DEVELOPMENT OF PLANTS 



355 



groups suggestive of the sori of the ferns, in some forms even 

 showing a rudimentary annulus. There is a considerable vari- 

 ation in the form of the sporophylls and the distribution of the 

 sporangia. For example, in Cycas, the megasporophylls are 

 loosely associated and only slightly modified, the sporangia being 

 developed on their margins (Fig. 245, 3.8). The microsporo- 



3B 



FIG. 245. Sporophylls and sporangia of the Cycads: 2, strobilus of Zamia. 

 2A, cross-section of strobilus of Zamia, showing artangement of microsporo- 

 phylls. 2B, microsporophyll enlarged, showing sporangia arranged in sori. 

 2C, sorus of three sporangia that have opened. 2D, microsporophyll of 

 Cycas. 3, cross-section of a strobilus of Zamia, showing arrangement of 

 megasporophylls. T,A, megasporophyll enlarged with two sporangia. The 

 one on the right shown in section; ms, megaspore; i, integument; sp, spor- 

 angium; m, micropyle. $3, megasporophyll of Cycas with laterally ar- 

 ranged megasporangia. H. O. Hanson. 



phylls are small and more compactly arranged, the sporangia 

 being associated in sori on the lower surface of the sporophylls 

 (Fig. 245, 2.D). In Zamia, the strobili and sporophylls are quite 

 suggestive of Equisetum, the sporangia being developed on the 

 inner side of shield-like sporophylls (Fig. 245, 2-3^!). 



The microspores originate by the division of certain cells just 

 beneath the epidermis and are discharged from the sporangium 

 very much as in the Ophioglossales. The megasporangia, 



