14 THE TREND OF THE RACE 
The plants resemble one another not because one is derived 
from the other, but because all are derived from a common 
source. 
Such a view of heredity, sharply opposed as it was to the older 
views that derived the offspring in some way from the various 
parts of the body of its parents, made the transmission of acquired 
characters improbable a priori. Weismann accordingly sub- 
jected the evidence for such transmission to a searching criticism 
and came to the conclusion that it was entirely inadequate. His 
attacks upon the Lamarckian theory which appeared in a series of 
essays, books and lectures nearly up to the period of his death did 
much to shake the faith of biologists in this at one time widely 
accepted doctrine. 
Weismann was not content simply to explain heredity as due 
to the continuity of the germ plasm, and to remove obstacles that 
seemed to lie in the path of that theory. He attempted to elabo- 
rate a theory of the composition of the germ plasm which would 
explain development, regeneration and various other phenomena 
in addition to heredity. Investigations into the structure of the 
cell and especially the peculiar behavior of the sex cells in matura- 
tion and fertilization had revealed a wonderful and orderly series 
of phenomena of which even the contemporaries of Darwin had 
little dreamed. Weismann was among the first to interpret the 
significance of these striking phenomena for the theory of heredity 
and evolution, and the essential part of his early theory of the 
significance of maturation has received a remarkable verification 
by recent work. More than any one else Weismann is responsible 
for directing attention to the importance of the combination of 
the study of heredity with cytology which has lately been produc- 
tive of such brilliant results. Many of the features of his elabo- 
rate speculative system have been rendered improbable (though 
we may not say definitely disproved) by experimental work; others 
have proven to be remarkably prophetic; on the whole, the body 
of doctrine which may be designated as Weismannism, as it was 
by Romanes, has afforded a great stimulus to the study and 
interpretation of the facts of heredity, and has left its very 
