726 THE AMERICAN NATURALIST. [You 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 denned 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 

 oospheres 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 



