SPERM ATOPHYTES 



193 



the stem from their emergence 

 from the cylinder. These leaf 

 traces curving about through 

 the cortex are called girdles, 

 and are conspicuous objects in 

 any cross section of the stem 

 (fig- 438). 



Leaves. — The leaves are very 

 large, pinnate, and generally 

 leathery. The mesophyll is 

 peculiar in containing cells 

 elongated parallel with the leaf 

 surface, and so loosely arranged 

 as to appear like bridles of 

 tissue traversing a large cavity. 



Strobilus. — The strobili are 

 dioecious, in striking contrast 

 with those of Bennettitales, in 

 which the staminate and ovu- 

 late structures are not only on 

 the same plant, but also in the 

 same strobilus. 



«:'-■■ 



Fig. 436. — Zamia (from Florida), showing 

 small, tuberous, mostly subterranean stems, one 

 bearing a staminate strobilus. 



Fig. 437. — Zamia, bearing an ovulate strobilus. 



Staminate. — In the staminate strobili the sporophylls are closely 

 imbricate (figs. 436, 439), narrowed below, and broadened above into 



