Inheritance of Acquired Characters 25 



whole result resembles the selection of a few resistant 

 individuals from an impure strain. 



3. Effect of use and disuse. — Weismann dis- 

 credited this behef, which was the foundation of La- 

 marck's theory of evolution. He was successful in 

 practically all the cases that had been presented for 

 animals. In plants, of course, it would be hard to find 

 anything exactly analogous to the use and disuse of parts 

 in animals. One fact, however, may be mentioned which 

 is a common experience of botanists. Functionless 

 organs gradually become aborted, becoming mere ves- 

 tiges, or even suppressed. A study of the organogeny 

 of a flower shows that when a floral member is belated 

 in its development it is destined sooner or later not to 

 appear at all. The Weismannian explanation of this 

 situation would probably be as follows. A given species 

 has given a nutritive capacity; the less it draws upon 

 its nutritive capital for the development of one organ 

 the more it can afford to expend upon the development 

 of other organs. When an organ becomes fimctionless 

 it no longer has any survival value; survival is then 

 dependent upon the relative development of the other 

 organs. Certain variations develop the functionless 

 organ less than usual and therefore develop the other 

 organs more than usual, and under the new conditions 

 these variations will survive and the others be eliminated. 



This is a description of natural selection by which 

 functionless organs become more and more aborted and 

 vigorous organs survive, but such an explanation is 

 rather imaginative. 



4. Disease transmission. — Roughly speaking this 

 may be grouped as (i) infection by bacteria or fungi, and 



