70 HEREDITY 



of reproduction ; though these tissues belong to the 

 individual body of the plant, and are definitely dis- 

 tinct from the special reproductive tissues which con- 

 tain the " germ- plasm" of Weismann. Further, in 

 many of the lower animals and plants, budding is 

 possible in almost any part of the body. Further, 

 there are the facts of regeneration and repair, which 

 have compelled Weismann to introduce an extremely 

 hypothetical and artificial sub- section into his theory 

 of the continuity and fundamental distinctness of 

 the germ-plasm. But the facts cited by Hertwig 

 are intelligible if we assume that every cell of the 

 body " contains the germinal material for every part 

 of the body, and thus, on the call of special con- 

 ditions, can become a germ- cell again." Hertwig 

 supports his theory by very numerous and varied 

 experiments. These appear to show that when 

 embryonic organisms are exposed to abnormal con- 

 ditions their cells can be made to undergo unusual 

 forms of development and take on functions other 

 than those observed in other conditions. The in- 

 ference is that no particular cells are unalterably 

 predestined for the reproductive or any other 

 function, and that the environment can cause this 

 or that cell, or collection of cells — according to 

 circumstances — to devote itself to the functions of 

 the '■ germ- plasm." 



It is not here proposed to attempt the recon- 

 ciliation of the diverse views of Weismann and 

 Hertwig. The writer's duty is rather to note the 

 existence of these differences of opinion. If the 

 theory of Weismann should appear to the reader 

 to have received undue consideration in these pages. 



