888 The American Naturalist. [November, 
to call attention to some of the processes of nutrition with 
reference to their import as causes of variation, or the origin 
_ of new characters that may be made available through natural 
selection in the evolution of plants and animals. 
The inheritance of acquired characters has been called in 
question by Weismann, and positively denied by those who 
accept his theory of the continuity of the germ plasma as 
originally formulated, and all inheritable variations are 
assumed to be the result of fortuitous changes in the reproduc- 
tive germs. 
The advocates of this theory confine their attention almost 
exclusively to gross morphological characters which have been 
developed and fixed through an accumulation of numerous 
slight variations for many generations, and ask for direct 
proof of the complete transformation of these stable characters 
by changes in the habits of a single individual, while the 
abundant evidence of physiological, or functional changes in 
nutritive processes which must be considered as the necessary 
precursors, and probable causes, of morphological variations, 
is claimed to be inadmissible. 
The processes of metabolism in the nutrition of plants and 
animals, as now interpreted by physiologists, furnish a rational 
explanation of the manner in which the reproductive germs 
may be influenced by functional adaptations of organisms to 
their environment, which are admitted to be causes of indi- 
vidual variations; and theories of heredity and evolution in 
which these physiological factors are not taken into considera- 
tion cannot be accepted as a satisfactory solution of the prob- 
lems presented. 
Omitting subordinate details which represent the separate 
links in the chain of events, the processes of nutrition may be 
summarized in general terms as follows: In plants the chemi- 
cal elements, and binary compounds on which they feed, are 
built up by successive steps of increasing complexity and insta- 
bility into protoplasm, with a storing of the energy made use 
of in the constructive process, which is derived from the heat 
and light of the sun. The constructive processes are expressed 
