1922] RANDOLPH—MAIZE 349 
EPIDERMAL CELL INCLUSIONS.—In maize the epidermal cells 
of leaves rarely contain plastids; if present at all they are few in 
number. Certain very characteristic structures are present, how- 
ever, which will be discussed only briefly, inasmuch as they seem to 
have no direct bearing on the problem of chlorophyll development. 
The epidermal cells of the meristematic region may be studied 
without removing them from the remainder of the leaf tissue. 
Their walls are not heavily cutinized during their early development, 
and the cells beneath are sufficiently transparent to permit a 
careful examination of cytoplasmic structures. The cytoplasm 
is limited to the parietal region of the cell, except for strands which 
pass through the large central vacuole to the region occupied by 
the nucleus near the inner wall. The cytoplasm of cells near the 
tip of embryonic leaves contains minute granules and short rods 
(fig. 47). These bodies are very numerous, and are carried rapidly 
about by the flowing cytoplasm, both rods and granules continually 
changing their positions. In older cells, that is, those farther 
removed from the tip, the rods are longer and more numerous 
(fig. 48). In still older cells many elongate filaments are to be 
found, as well as numerous granules and short rods (fig. 49). Cells 
have been observed in which even the elongate filaments are 
actively translocated by the cytoplasm; a single one may thus be 
observed for some time. This phenomenon furnishes definite proof 
that the filaments are structurally distinct elements, and not merely 
lines of flow, or other artifacts due to fixation. The fact that the 
filaments are longer and more numerous in the older cells than in 
meristematic cells suggests that they have resulted from an elonga- 
tion of shorter ones, and that these in turn may have originated 
from the granular bodies. Convincing proof of their division has 
not been obtained. A small number of colorless bodies which 
resemble the partly developed plastids of mesophyll cells are also 
found in these cells, but mature green plastids are rarely present. 
In addition to these structures, oil globules are present which may 
be distinguished by their greater refringence in living cells and by 
their characteristic reaction to osmic acid. The relation of these 
structures found in epidermal cells to the proplastids of esis 
cells will be discussed later. 
