38 Gibbs.— Notes on the Development and Structure of 
consistency, and quite at the base active cell division goes on, till maturity, 
when all the cells contain starch. This perisperm exercises a mechanical 
influence on the shape of the embryo-sac. The thin cytoplasm of the same 
has no effect on the dense contents of these cells (/r//2. Fig. 4). Careful 
investigation shows no sign of digested cells on the convex portion of 
the perisperm cells of the nucellus. Increase of breadth being thus effec- 
tually prevented on each side by the limits of the perisperm and testa 
respectively, the necessary expansion of the embryo-sac must take place 
in length and the natural effect of such a rigid mass of tissue is to increase 
the convexity of both embryo-sac and embryo. Hegelmaier ( 12 ) explains 
this development as a ‘ crescent-shaped portion of the nucellus which 
prepares itself for solution,’ but that is perhaps rather an arbitrary method 
of description. Before fertilization, the whole nucellar tissue is homogenous. 
After fertilization, starch localization takes place, which, as we have seen, 
affects certain cells of definite layers ; but the fact that the layers digested 
during the growth in length of the embryo-sac are not specialized as 
storage tissue, hardly justifies one in saying they are ‘ prepared for solution.’ 
Available for solution would be an expression more consistent with the 
facts, as the layers in question differ in no sense from the peripheral nucellar 
layers, which are constantly digested during the growth of the embryo-sac. 
Peripheral layers of the nucellus . The peripheral layers of the nucellus 
are four to five cells thick before (PL V, Figs. 6 and 7, per. /.) and just after 
