726 THE AMERICAN NATURALIST. | [Vor. XXXIX. 
inclusions occupy small spaces in the trophoplasm which are 
essentially vacuoles. There is also a class of granular inclusions 
of a proteid nature which probably represent material in very 
close organic relation to the substance of protoplasm. Tropho- 
plasm does not then have so clearly defined a type of structure 
as do the other regions of the protoplast but it is hardly probable 
that its essential nature changes very materially throughout the 
life history. The organization of trophoplasm is itself a matter 
of dispute but the prevailing views favor an alveolar or foam 
structure with a fibrous character at times somewhat resembling 
the texture of sponge. 
Ever since the classical investigations of Schimper upon the 
plastid it has generally been held that these structures are per- 
manent organs of the cell, reproducing by fission, and carried 
along from one cell generation to the next with as much per- 
manence as the nucleus. Schimper discovered plastids in the 
oóspheres of certain spermatophytes and in a variety of embry- 
onic tissues and concluded that the structures passed from 
parents to offspring as leucoplasts when no trace of color could 
be found in the reproductive cells or embryonic tissues. There 
has been, however, no systematic study of the plastid through- 
out the life history of higher plants and in most of the green 
thallophytes there are reproductive phases, such as resting 
spores, where we have no knowledge of the structure or distri- 
bution of the chromatophores in the cell. It is very important 
that the plastid be investigated with the same degree of atten- 
tion which has been given to the nucleus, and that it be fol- 
lowed through all periods of the life history in forms where the 
color becomes greatly modified or is absent in the reproductive 
cells and embryonic (meristematic) regions of the plant. Any- 
one who has studied the embryonic tissues of plants will realize 
the difficulties of the investigation which will probably involve 
the development of methods of technique, especially of staining, 
somewhat different from those generally employed in cell 
studies. 
We may now consider the elements in the nucleus and their 
behavior during ontogeny. This is one of the most interesting 
subjects in cell studies, for the importance of the chromosomes 
