HEEEDITY 



He calls them mutations, and regards them as 

 the sole means of evolutionary progress. But 

 it is a peculiarity of his mutation theory that 

 it regards only large changes in unit-characters 

 as having any permanency, namely, such 

 changes as mean a practical making over of 

 the character. To borrow a figure from Bate- 

 son, just as the gas carbon monoxide, C 0, 

 may change into a very different gas, carbon 

 dioxide, C 2 , by taking up a single atom 

 of oxygen, but can make no less extensive 

 change, since oxygen atoms do not split; so, 

 according to De Vries, a unit-character may 

 not change unless it changes profoundly. Vari- 

 ous circumstances may modify the degree of 

 its expression, but these are without perma- 

 nent effect, since the character itself remains 

 unchanged. 



But there are both a priori and experimental 

 grounds for questioning the correctness of 

 De Vries ' conclusions. It is known that the 

 chemical compounds within the germ-cells are 

 not so simple in composition as C and C 2 . 

 They are very complex substances, made up, 

 it is thought, of very many atoms, often hun- 



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