350 Mot tier . — On Certain Plastids , with Special Reference to 
Zea Mays L. 
For study a variety of sweet corn known as Golden Bantam, and an 
unnamed variety of starchy dent corn were selected. 
The endosperm of Zea develops from the periphery towards the 
centre, but the meristematic region is at the periphery ; consequently the 
younger cells are not next to the embryo. Soon after the cavity of 
the embryo-sac has become filled with endosperm, and the embryo has 
reached a considerable size, the several parts having been differentiated, 
the outermost layer of the endosperm, the aleurone layer of the mature 
grain, is differentiated as a definite and sharply defined row of cells, isodimen- 
sional or somewhat elongated (PI. XV, Fig. i). These cells show occasional 
periclinal divisions, but the more active meristematic cells, especially at 
a little later stage, lie just beneath, as seen in Fig. 2. With ordinary 
magnifications these cells present a dense granular appearance not unlike 
typical meristematic cells. A careful study shows, however, that in the 
groundwork of cytoplasm numerous very small and densely staining 
granules and short rods are present, along with others that are larger and 
globular (Fig. 1). The larger granules are not so numerous at this stage, 
and at an earlier stage they are not present, or, if present, not readily 
recognized. 
At a later stage the aleurone layer becomes more conspicuous, the 
rounded granules in the cells, among which are numerous very small 
granules and short rods, becoming larger and much more numerous. The 
outer wall of these cells begins to thicken at this stage (Fig. 2). Beneath 
the aleurone layer is a meristematic region about three cells in depth, in 
which the elements are flattened in a tangential direction, owing to rapid 
division in that plane (Fig. 2). In the first row of cells beneath the aleurone 
layer, protein granules are present, though fewer in number, together with 
the small rods and granules already mentioned. In the second and third 
layers, few of the larger, round granules are present at this stage, but the 
very small rods and granules are quite in evidence. Deeper in the 
endosperm the cells are large and relatively poor in contents (Fig. 5). 
They contain large vacuoles and many starch grains, especially in starchy 
corn. Figs. 2 and 5 were drawn from starchy corn. In some of the cells 
the nuclei do not present the smooth, even outline, but rather an irregular 
contour (Fig. 5). In the cytoplasmic groundwork, among the starch grains 
and in the cytoplasmic strands between the vacuoles, are numerous densely 
staining granules and short rods similar to those in the aleurone layer and 
in the meristematic region (Figs. 2 and 5). 
With further growth of the grain of corn, the cells of the aleurone layer 
rapidly increase in size, the walls becoming very thick, especially the outer 
and radial walls (Fig. 3). The aleurone granules have also increased greatly 
