346 BOTANICAL GAZETTE [MAY 
concerned with the formation of chloroplasts, the term ‘‘pro- 
plastid”’ will be used for such bodies. Other cytoplasmic granules 
and transitory accumulations not concerned with the development 
of plastids may be present later. Oil globules which can be dis- 
tinguished from the proplastids by their characteristic highly 
refractive appearance and microchemical reaction, and other 
metaplasmic masses in the vacuole (fig. 5) are to be found at certain 
stages. The chemical nature and significance of these bodies are 
not known, and a detailed consideration of this phase of the problem 
is hardly within the scope of the present work. 
The position and behavior of the proplastids during cell division 
have been observed in the living cells. There is apparent no 
definite sorting out of equal numbers to daughter cells, or more 
active division of individuals during this period. The proplastids 
are grouped at opposite ends of the cell during mitosis, and their 
passive distribution to the daughter cells seems to depend wholly 
upon their chance positions in the cytoplasm at the time of cell- 
plate formation. 
PLASTID DEVELOPMENT.—The formation of mature functional 
plastids from minute granular proplastids may readily be followed 
in the subepidermal cells of the tips of leaf buds forming from the 
apical meristem. The earlier transitional stages are present in 
the meristematic cells near the apices of successively older seedling 
leaves which are growing rapidly, and which are not yet exposed to 
sunlight. Later stages are found in the leaves which are about to 
emerge from the surrounding sheath. In passing from the tip of 
such a leaf toward a point somewhat below the tip a series of 
stages may be observed. Numerous well developed plastids are 
present in the mesophyll cells of fully exposed seedling leaves. 
In leaf tissue recently formed from the apical meristem the 
cells contain some proplastids which have increased noticeably in 
size, and others similar in size and appearance to those found in 
younger cells (fig. 2). Vacuoles are present in these cells, and the 
cytoplasm becomes more or less limited to the region surrounding 
the nucleus and to the periphery of the cell, with connecting strands 
between. Cytoplasmic streaming, which is commonly active at 
these stages, carries the proplastids about through the cell, even 
the largest ones being translocated in this manner. 
