SPERMATO PHYTES 
209 
FIG. 468. Ovulate strobili of Ginkgo, borne in clusters 
on dwarf branches, and each bearing two ovules. 
Ovulate. The ovulate strobili are also borne on the dwarf branches 
and are very much reduced (fig. 468). A strobilus consists of a long 
stalk, near the tip of 
which usually two ovules 
are borne, only one of 
which usually matures 
a seed (fig. 469). At 
the base of each ovule 
there is a little cupule or 
collar, which is the rudi- 
ment of the sporophyll 
(fig. 470). Sometimes 
there are three or four 
ovules on a strobilus, 
and sometimes the collar 
becomes leaflike; so it 
is evident that the strobilus is remarkably reduced, usually producing 
only two ovules upon very rudimentary sporophylls. 
Ovules. The ovules resemble in general structure those of Cor- 
daitales and the cycad line al- 
ready described (fig. 470), with 
the three-layered integument 
(outer fleshy, stony, and inner 
fleshy layers), the nucellar beak, 
and the pollen chamber ; but the 
set of vascular strands, which in 
the groups referred to traverse 
the outer fleshy layer, are not 
present in Ginkgo, only the inner 
set appearing in the inner fleshy 
layer. 
The megaspore mother cell is 
first observed deep within the 
nucellus, and it becomes invested 
by a distinct zone of glandular 
tissue. This glandular zone is 
FIG. 469. Ovulate strobili of Ginkgo digestive in function, invading 
bearing developing seeds: the strobili to the ,i j- 
right have developed single seeds; those to and Destroying the surrounding 
the left have developed both seeds. 
tissue of the nucellus. Surround- 
