Nichols, A morphological study of Juniperus communis var. deprcssa. 203 
develop until the following season. The earliest stages to be 
described are from material collected February ll th and kept in- 
doors for two days. The differentiation of the tapetnm and inner 
layer of the sporangium wall from the sporogenous complex takes 
place during the first week in April. A prolonged period of growth 
then follows, accompanied by cell division, culminating about May 1 st 
in the formation of the microspore mother cells. 
During the winter the lower part of the sporophyll is com- 
posed of meristematic cells of uniform size and structure, while 
the upper portion is already occupied by large yacuolate cells con- 
taining numerous compound starch grains. The latter are conspicuous 
in many of the vegetative cells of the sporophyll until shortly 
before pollination. The archesporium first becomes recognizable 
as a plate of radially elongated hypodermal cells, four to six in 
number when viewed in longitudinal section (fig. 5). Structurally 
there is little to distinguish them from the adjacent sterile cells 
save their somewhat denser cytoplasm. This layer soon divides 
by periclinal walls (fig. 6), and the archesporium continues to in- 
crease in size by the growth and division of its cells without any 
differentiation becoming apparent. By the time the stage shown 
in fig. 7 is reached the archesporium is without difficulty distin- 
guishable from the vegetative tissue of the sporophyll through the 
denser contents of its cells, while the base of the sporophyll has 
begun to bulge slightly in the region where the microsporangium 
is being developed. 
After a considerable mass of cells has been formed those 
of the outer layer divide, and two layers of tabular-shaped 
cells are cut off, which completely enclose a central mass of cells 
(fig. 8). The latter may be termed the primary sporogenous cells, 
since after a period of further growth and division they give rise 
to the spore mother cells. The inner of the two enveloping layers 
becomes the tapetum, while the outer layer develops into what 
is usually termed the inner layer of the sporangium wall. This 
latter layer, if viewed in a not quite mature sporangium, does 
appear to be a part of the wall, since, after the breaking down 
of their contents, the crushed cells form a thin layer which is 
closely appressed to the outer layer of the wall (figs. 11, 12). 
Morphologically, however, it is more closely correlated to the ta¬ 
petum, both tissues being derived in the manner described above 
from the archesporium, while the outer layer of the wall has quite 
a different origin, as will be seen presently. Moreover the sub- 
sequent history of this layer shows that physiologically also it is 
a sort of accessory tapetum, contributing nourishment to the de- 
veloping spores and eventually disappearing entireiy. An analogous 
case has been noted in Stcmgeria (Lang 1897) where the inner 
layers of the wall are disorganized during the growth of the micro¬ 
sporangium, and similar conditions are found in other Gymnosperms. 
Soon after the differentiation of the tapetum and the inner 
wall layer from the sporogenous cells the majority of the sterile 
cells in the lower part of the sporophyll become vacuolate. Certain 
