202 BOTANICAL GAZETTE [SEPTEMBER 
embryo, owing to shrinkage of the material from lack of penetra- 
tion of the fixing fluids. The growth of the embryo proceeds 
very slowly as compared with the endosperm, and it is but a small 
spherical mass of cells when the latter has come to occupy the whole 
central region of the carpellary tissue (fig. 51). At first the embryo 
is intimately connected with the endosperm, from which it gradually 
separates as development continues. The micropylar end or the 
radicle is first freed, while the cotyledons are last to be separated. 

The embryo is strictly dicotyledonous, and when mature is almost | 
entirely imbedded within the endosperm (fig. 52). The endosperm 
enlarges at the expense of the adjacent tissues. Soon after the 
origin of the embryo, it begins to elongate in the direction of the 
longitudinal axis of the ovary and at the same time becomes 
flattened in the plane of flattening of the spike. Growth at first 
is almost entirely upward and the apex of the endosperm reaches 
to the base of the style. Later, by gradually digesting the remains 
of the placenta, it advances downward into the plate of tracheids 
at the base of the ovary. The endosperm thus replaces the entire 
axial region of the flower and lies in direct ‘contact with the vascular 
traces of the carpels (figs. 20, 21, tc) which later form a part of the 
covering of the seed (figs. 22, 66). 
The endosperm is composed of large parenchyma cells, the walls 
of which are relatively thin and of a most uniform thickness. The 
cells of the external layer are largest, attaining their greatest size 
at the base of the endosperm (figs. 53, 54). They are not specially 
modified for protection as in Phoradendron flavescens, and do not 
form a true epidermis. They fit loosely together and seem to have 
an absorptive function. This is especially true in the basal portion 
of the endosperm, in which the outermost layer of cells contains 
large nuclei and very fine granular cytoplasm which stains brownish 
yellow in iodine (fig. 53). Since these cells are in direct contact 
with tracheid cells, the greater bulk of food passing into the endo- | 
sperm must enter through them. Hence they are considered as 
being primarily absorptive in function. The fact that the cells of 
the outer layer fit loosely together also indicates that they are 
capable of readily absorbing water when germination begins. 
Sections of seeds which had just begun to germinate showed that 
