126 BOTANICAL GAZETTE [AUGUST 
off a cap cell. I have sought in vain, however, to establish that 
the first two are sister cells. When the sporangium consists of 
from four to six cells (figs. 6, 7, 8), the hypodermal cells assume 
a different appearance when stained, which distinction is main- 
tained thenceforth in the development, and establish their 
identity as primary sporogenous cells. There is no apparent 
regularity in the order or plane of their division, with the excep- 
tion above stated. The tapetal cells are differentiated very 
early in the history, and are the peripheral sporogenous cells 
which assume a more symmetrical shape and regular arrange- 
ment (fig. zo). A few of the cells in this layer, lying directly 
above the pedicel of the sporangium, appear to be derived from 
the vegetative cells in that region, and are not the lineal descend- 
ants of the archesporial cell. 
Simultaneously with the differentiation of the tapetum the 
sporangium wall divides into two layers by anticlinal partitions 
(fig. 10,. The outer layer soon surpasses the inner in the size 
of its cells (fig. rz). <A pedicel develops by the multipli- 
cation of the sterile cells next to the axis and beneath the 
sporogenous mass. The megasporangium cannot be distinguished 
from the microsporangium until the moment when the cells of 
the sporogenous tissue cease to divide, separate from one 
another, and float in the sporangium. At this period, if one or 
two cells are more regular in form, stain more deeply, and 
possess a larger nucleolus, they are megaspore mother cells 
( figs. 13, 35,36). The microspore mother cells are not dis- 
tinguishable until the karyokinetic figures develop that precede 
their division into spores. A comparative count of the micro- 
spore mother cells in this stage and the cells in a corresponding 
megasporangium indicates that there is at least one more period 
of cell division in the former than in the latter. A cytological 
study may determine other means of identifying the two. 
MEGaspoRES.—The megaspore mother cell becomes nearly 
isodiametric, enlarges, stains deeply, and lies near the tapetum 
( figs. 13, 35). Apparently the mother cell never originates far 
within the sporogenous tissue but always near its periphery. 
