142 
WALTER P. THOMPSON 
5. Staminate Flower and Microsporangium 
The young stamen is completely enclosed in an envelope known 
as the perianth which becomes ruptured at maturity. Stamen and 
envelope together constitute the staminate flower. The mature 
stamen resembles that of Angiosperms very closely except that it 
bears two sporangia instead of four. When it is remembered that 
the microsporophyll of no other group of Gymnosperms approaches 
this form, it seems that the resemblance to the Angiosperm stamen 
has not been sufficiently emphasized. 
In the course of development the numerous flowers of a group 
arise in basipetal succession. Within a single collar one may find 
many stages. In the case represented in figure 4 the uppermost 
flower has already developed a perianth while the lowermost is a 
barely recognizable rudiment. In figure 5 the uppermost flower is in 
the mother-cell stage while the lowermost is just beginning to form a 
perianth. It is not possible to say that either perianth or stalk arises 
first because they arise together in a single rudiment from which the 
perianth becomes separated later by a circular depression (fig. 5 at 
the bottom). Then the perianth elongates and closes over the central 
rudiment of stalk and sporangia. 
The archesporium consists of a hypodermal layer of cells which 
first becomes recognizable shortly after the perianth is differentiated 
(fig. 6). As usual it divides to form a primary parietal layer against 
the epidermis (fig. 7) and the primary sporogenous cells. The parietal 
layer divides again periclinally producing two layers of cells between 
the epidermis and tapetum (fig. 8). No further divisions take place 
in the wall cells. Indeed in some cases even the second layer is not 
formed and in other cases only a few of the primary wall cells appear 
to divide again. In all cases the cells of the inner layer become more 
or less rounded and separate from each other (fig. 9). Later the cells 
of the outer layer also become rounded at the ends. All the parietal 
cells then gradually degenerate leaving only a thin band of granular 
substance against the epidermis. Consequently there is nothing 
resembling the endothecium of Angiosperms. Indeed in the mature 
sporangium the spores are enclosed in a single layer of cells, the 
epidermis. 
In the meantime the primary sporogenous cells have been dividing 
and have formed a considerable mass of tissue. Before the cells of 
