9 
Embryo in Lilaea subulata , H. B. K . 
a single primary archesporial cell ; indeed it is quite impro- 
bable that they all originate from a common mother-cell. As 
they become older, however, they become noticeably larger 
than their neighbours, and show the usual dense contents and 
large nuclei (Figs, 9, 10). However, even in these stages the 
transition from genuine sporogenous tissue to the tapetal 
cells is somewhat gradual. The latter are derived mainly 
from the periblem, but functionally, at least, some of the 
plerome-cells must be regarded as tapetal. 
As the stamen grows, the four masses of sporogenous tissue 
become very clearly defined. Each group of sporogenous 
cells is surrounded by about three, or in places four or five, 
layers of cells which separate it from the epidermis. The 
cells, which at first are much alike, later show considerable 
differentiation. 
Fig. io shows a longitudinal section of a loculus shortly 
before the separation of the sporogenous cells. The epidermal 
cells are now much elongated, but are very little deeper than 
they were in the very young stamen. Under the epidermis 
is a layer of somewhat swollen cells which, with the epidermis, 
persists as the wall of the mature loculus. Within this second 
layer is a third one, composed of very much compressed cells 
(c), which with a fourth layer ( d ) make up the tapetum. The 
layer d has larger cells which resemble the sporogenous cells 
in the character of their contents. 
The sporogenous cells ( sp .) have the usual characters of 
such cells. They are thin-walled, isodiametric, with abundant 
granular cytoplasm and large nuclei. The nucleoli are con- 
spicuous and the chromatin abundant. The nucleus, in 
material fixed with chromic acid, usually shows a conspicuous 
areola about the nucleolus. On the inner side of the loculus 
especially, the tapetal cells encroach upon the sporogenous 
area, and there are cells which are intermediate in character 
between the perfect sporogenous cells and those of the 
tapetum. These are probably to be considered as potentially 
sporogenous cells which do not, however, develop into spores, 
but become broken down and serve, like the true tapetal cells, 
