1922] RANDOLPH—MAIZE 347 
In somewhat older stages (figs. 3, 4) the largest bodies remain 
stationary or nearly so, and are not affected by the cytoplasmic 
streaming. A grouping of proplastids of various sizes is often seen 
in certain parts of the cell. This most frequently occurs in the 
parietal portion of the cytoplasm, whereas in certain other cells 
there may be a grouping of almost all of the proplastids about the 
nucleus (fig. 51). In the present study these and other modes of 
grouping have not been correlated with any other phenomenon of 
cell activity. 
Evidence for the division of the developing plastids is not 
difficult to obtain in the later stages (fig. 5). Cytoplasmic stream- 
ing is not so active in such cells, and the proplastids which have 
reached a size of 2 uw or over may frequently be seen in the process 
of division. 
A variation in the size of the proplastids which are present in 
a single cell is markedly characteristic of the tissues studied. In 
such a cell as that of fig. 6 there is a close intergrading series, from 
proplastids which are so small as to be barely visible, up to others 
which have a diameter of 4.5-5 u. The largest proplastids of this 
cell appear faintly green. The presence of these transitional stages 
within a single cell furnishes convincing proof of the origin of chlo- 
roplasts from bodies which at first are scarcely visible, and which 
one is led to believe may even arise de novo from the cytoplasm. 
In no case has the presence of green color been found to be asso- 
ciated with the proplastids until they have reached approximately 
one-half of the size and shape of mature functional plastids. The 
appearance of starch in the developing proplastids, which some- 
times occurs, is perhaps associated in some way with chlorophyll 
formation. 
The final stages in the maturing of chloroplasts may be ob- 
served in the cells near the tip of a seedling leaf which is about 
to emerge from the enveloping sheath (figs. 7, 8). Subepiderma] 
cells near the apex contain a small number of partially developed 
plastids in which chlorophyll is present, and many smaller pro- 
plastids of varying size (fig. 7). Farther back from the tip the 
mesophyll cells contain an increasingly large number of nearly 
mature plastids, the majority of which are markedly green, and a 
diminishing number of proplastids (fig. 8). Finally, in the cells of 
