52 BOTANICAL GAZETTE [JANUARY = 
the sporangium that will finally function appears in advance of the mucilage 
ducts, or the two may start together, but generally the ducts are formed 
before the functioning sporogenous tissue is very evident. By August 8 the 
sporophylls at the base of the strobilus show the formation of the stalk and 
the elongation of the functioning sporangium (fig. 3), while the sporophylls 
from the base to half-way up the strobilus have well-developed mucilage 
ducts. The stalks are formed by an increase in the number of cells as well 
as by elongation of the cells. By August 20 all the sporophylls have stalks 
and mucilage ducts, but the functioning sporogenous tissue is conspicuous 
only in the lower sporophylls. Early in September (fig. 4) the strobili have 
reached a length of 3™™, the sporophylls have the typical shape, the mucilage 
ducts are enormous, and the cells of the sporogenous mass are separating 
for the mother cell stage, which the oldest sporangia reach before winter, 
according to SPRECHER? (p. 156). Material that I collected in April shows 
some sporangia in the mother cell stage and others with tetrads formed. 
Development of the functioning sporangium 
The early development of the functioning sporangium is probably like 
that of the cycads,3 though I have not yet been able to determine that the 
archesporium starts as a single cell, but stages like that in jig. 5 probably 
indicate that a single cell has divided anticlinally and then periclinally. 
Sometimes the order seems to be reversed. The outer cells are the primary 
wall cells, giving rise to several layers of wall cells with scanty cytoplasm; 
the inner are the primary sporogenous cells, by further division producing 
a large mass of sporogenous, cells with dense cytoplasm, larger nuclei with 
heavily staining chromatin, and frequently conspicuous nucleoli. In the 
mature sporangium the hypodermal layer of cells and the layer below tt 
have thickening bands in the walls, and in the upper part of the sporangium 
near the mucilage duct the walls of deeper cells are also thickened. In this 
respect the microsporangium of Ginkgo differs from the microsporangium 
of all other gymnosperms and is like that of angiosperms. 
The tapetum seems to come entirely from the sporogenous mass. 
Development of the mucilage ducts 
The upper, sterile part of the sporophyll is developed into a humplike 
projection called by CELAKOvSK¥4 (p. 283) a crest (crista). In this are 
2 SPRECHER, ANDREAS, Le Ginkgo biloba L. pp. 206. figs. 225. Geneve. 1907- 
3 SMITH, FRANCES GRACE, Morphology of the trunk and development of the J 
microsporangium of cycads. Bot. GAZETTE 43:187-204. pl. 10. 1907. 
4 CELAK Kovsky, L. J., Die se der Sporangium von Ginkgo biloba L- 
Oesterr. Bot. Zeitschrift 50: 276-283. 19 
