SPERMATOPHYTES 
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 
FIG. 436. Zamia (from Florida), showing 
the same plant, but also in the 
small, tuberous, mostly subterranean stems, one 
same Strobilus. bearing a staminate strobilus. 
FlG. 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 
