426 BOTANICAL GAZETTE [DECEMBER 
layers to the root cap. The pressure, crowding the coleorhiza 
against the micropylar end of the seed, causes an irregular jagged 
fracture of the stony coat of the seed, through which the embryo 
emerges. It is only after the fracture is large enough to permit 
the exit of the embryo that the root cap pierces the central portion 
of the coleorhiza, the thick-walled cells of which may be seen 
clinging to the root in threadlike masses even after the axis of 
the seedling has become vertical. 
The late. differentiation of body regions is a noticeable feature 
of the cycad embryo. At the stage shown in fig. 15, not only is 
the differentiation into periblem and plerome still incomplete, but 
even the dermatogen is not yet differentiated, as may be seen by 
the periclines in the cotyledons and especially in the stem tip 
(figs. 15, 17). Perhaps the importance of division by anticlines 
only has been overestimated, for in this embryo the outer 
layer looks like a dermatogen long before the periclines cease to 
appear. 
A general view of an embryo at the stage shown in fig. 15 may 
be seen in the accompanying diagram (fig. 16), drawn from the 
same preparation. Just below the suspensor with its large mucilage 
cavities is the swollen coleorhiza. Starch is found in the suspensor, 
but is most abundant in the peripheral and lower regions of the 
coleorhiza. Cell division is most active in the dotted region of 
the stem tip. While the general appearance of the mitoses is very 
different from that described for the free nuclear period, it is 
probable that the difference is not so great as it seems, for in fig. 
18 the spindle may mark the limit of the nuclear membrane. 
A diagrammatic section through a ripe seed is shown in fig. 19- 
The embryo extends almost the entire length of the seed, the cotyle- 
dons constituting the principal mass. The first functional leaf, 
if drawn on a large scale, would show the primordia of pinnules, the 
scale leaves not showing such a differentiation. The outer fleshy 
layer and the middle or stony layer (shaded) are easily distinguished, 
but the inner fleshy layer, while forming a conspicuous membrane 
containing the inner vascular system, is too thin to be shown in the 
diagram. Although the stony layer is quite thin in the region of 
the pit at the base of the seed, the cotyledons never emerge at 
