253 [Cope. 
1871.] 
And it may be said in conclusion that if the three principles, or if use 
especially, should be found to be inadequate to the service here demanded 
of them, it may be at least said that they or the last named, constitute 
the only controllers of growth force to any degree at all, with which we 
are acquainted. 
IV. ON GRADE INFLUENCE. 
The object of the present section is the attempt to discuss how the in- 
fluence of effort and use on the parent is placed in a position to be inher- 
ited by the offspring. 
A. Of the Nature of Grade Influence. 
In the first place, it is necessary to note the definition and character of 
grade influence. : 
a. Growth force uninfluenced by grade influence simply adds tissue 
either (a) in enlarging size, or (0) in replacing waste. Tt does this by re- 
peating the cell, by division, in localities which have already assumed their 
specific form. This form of growth force may persist throughout life, but 
with diminished energy in age. 
&. Grade influence directs growth force in building up the tissues into 
organs, and constructs the parts of the body successively to completion, 
the result expressing the type or grade of the animal or plant. Its 
energy terminates with maturity, except in cases of periodical reproduc- 
tion of sexual ornaments of the male (birds, deer), where it continues 
throughout life, appearing at regular intervals. 
But it has occurred in acceleration that instead of a simple repetition of 
the ultimate histological element of an organism, in adding to its amount, 
itadds a completely organized part of the structure, as a tube, a phalange, 
a digit, a limb or an arch; an ocellus or a tooth. For instance, in the 
genus Amblystoma, one section possesses four phalanges on the longest 
digit ; another section exhibits but three. In the species A. mavortium, 
some individuals have the small number of phalanges, but the majority 
possess the larger number. As all are of common parentage a whole pha- 
lange has been lost or added. The explanation of this phenomenon is © 
essential to the comprehension of the or/gin of type structures. 
*In plants, growth nutrition continues throughout life, but in the 
higher plants it is more active during the earlier years in perennial 
species, additions te size becoming less and less marked with increasing 
‘age. Grade nutrition also persists throughout life, but is chiefly active 
during a short period only of every year, or during flowering and fruit- 
ing. Not only in the production of the reproductive organs, but also in 
the yearly additions to other typical parts of the plant, grade-nutrition is 
active. 
*In animals, growth nutrition is more active in the early stages of 
life, but is continued throughout in the lower divisions ; in the highest, 
it is also continued throughout life, but there is a greater contrast between 
its results during youth, when nearly the whole size is attained, and dur- 
ing age, where the additions are much less. 
remeron ne 
