432 THE AMERICAN NATURALIST. [Vol. XXXVI II. 



to turn to any form of activity possible to the species. Portions 

 of the germ plasm are constantly being detached from the main 

 stream and relegated to more or less special duties. Such pro- 

 toplasm becomes the body plasm, or soma, of the individual. 

 Specialized body plasm generally loses very shortly the reproduc- 

 tive possibilities of germ plasm, and in consequence must finally 

 die, for its nicely adjusted dependence upon surrounding cells 

 cannot last forever. Yet it has been one of the surprises of 

 biological science that specialized tissues may keep for a very 

 long time the reproductive qualities of germ plasm. Investiga- 

 tions on regeneration in particular have brought these facts con- 

 spicuously to the front. As an extreme example among plants, 

 it is known that even the epidermal tissues of leaves and scales 

 of certain ferns (Palisa, : oo) may sometimes retain the funda- 

 mental qualities of germ plasm and reproduce the plant. 



There are no visible characters that separate body plasm from 

 germ plasm, excepting, of course, when body plasm begins to 

 show signs of degeneration. Germ plasm may only be distin- 

 guished by its potentialities of growth and reproduction, potenti- 

 alities that cannot be accurately determined because the stimulus 

 to development is, in the last analysis, an external one and the 

 conditions which govern it may be so intricate as to escape close 

 scrutiny. 



Germ plasm is found in its most generalized condition in the 

 cells of growing points, in embryonic and meristematic regions, 

 and in the reproductive tissues. These tissues are well recog- 

 nized as the most favorable for cell studies because they present 

 most clearly the details of protoplasmic activities. Almost all 

 that we know of cell activities have come from investigations of 

 such regions. 



One of the first signs of that specialization which transforms 

 germ plasm to body plasm is the slowing up and final end 

 of nuclear and cell division. With this change come a great 

 variety of modifications (peculiarities of cell wall, plastids, cyto- 

 plasmic activities, etc.) which may be readily associated with the 

 particular work of that tissue. 



The vegetative activities of germ plasm are chiefly those of 

 growth, which in the end mean reproduction, the embryonic cells 



