DEVELOPMENT OF PLANTS 



323 



modified, the sporangia being developed on their margins (Fig. 

 245, 3$). The microsporophylls are small and more compactly 

 arranged, the sporangia being associated in sori on the lower 



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

 Zamia. 2.A, cross-section of strobilus of Zamia, showing arrangement of 

 microsporophylls. 2.B, microsporophyll enlarged, showing sporangia ar- 

 ranged in sori. 2.C, sorus of three sporangia that have opened. 2.D, micro- 

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

 rangement of megasporophylls. 3/4, megasporophyll enlarged with two 

 sporangia. The one on the right shown in section: ms, megaspore; i, 

 integument; sp, sporangium; m, micropyle. ^B, megasporophyll of Cycas 

 with laterally arranged megasporangia. H. O. Hanson. 



surface of the sporophylls (Fig. 245, 2D). In Zamia, the stro- 

 bili and sporophylls are quite suggestive of Equisetum-, the spo- 

 rangia being developed on the inner side of shield-like sporo- 

 phylls (Fig. 245, 2-3/4). 



The microspores originate and are discharged from the spo- 

 rangium very much as in the lower ferns. The megasporangia, 

 however, present several new departures that must be borne in 

 mind. A rather thick coat or integument covers the sporangium 

 save for a small opening called the micropyle (Fig. 245, 3^4). 

 The integument will be a feature in all the succeeding groups and 



