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 defijiitely 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 



