364 BOTANICAL GAZETTE [may 
ment. Although they can be so studied in the living cells, it is 
nevertheless necessary to employ methods which will not only 
permit one to view the living cell for a moment in the “living” 
condition, but which will allow continued observation of the 
actively functioning cell over a considerable period of time, thus 
avoiding alteration in the cytoplasm which may be brought about 
very quickly when the living tissue is improperly handled. 
The proplastids appear in their initial stages as refringent 
globules of varying size, always sharply distinct from the ground 
substance of the cytoplasm. They are constantly changing their 
position in the embryonic cells, being often carried about rapidly 
y the streaming cytoplasm. This phenomenon makes it appear 
certain that even the most minute of the proplastids are special — 
structures distinct from the principal mass of cytoplasm in which 
they lie. Particular attention has been devoted to these minute 
proplastids which lie just within the lower limit of the range of 
visibility. They have been examined with lenses of very high 
resolving power (Zeiss apochromatic objective, 2 mm. N.A. 1.40 
and compensating ocular 6), and their activity has been repeatedly 
watched very closely. Very important questions concerning the 
ultimate nature and significance of proplastids are here involved, 
and will be discussed in another connection later. The subsequent 
enlargement of the proplastids to form chloroplasts can be traced 
step by step throughout their course of development, abundant 
material being readily obtainable from young seedlings. . 
Although comparatively few investigators have based their 
interpretations mainly on the study of living cells, they agree 
with the present writer in reporting the presence of such minute 
bodies in the living meristematic cell. In older cells, however, 
many phenomena have been described which the present writer 
has not observed, although this may be due in part to the fact that 
this study has been limited largely to mesophyll cells. The few 
observations made on the cells of other tissues indicate that addi- 
tional types of cell elements and modes of behavior may be present 
there. For example, conditions similar to those figured by GUIL- 
LIERMOND in epidermal cells of flower petals and other floral organs 
have been seen in the epidermal cells of maize, but not in the 
mesophyll cells. 
