26 Plant Genetics 



(2) some inherent organic weakness. Since the latter 

 condition is chiefly serious only in inviting attacks 

 by bacteria or fungi, we are concerned chiefly with 

 diseases caused by these pathological forms. Realizing 

 this, true inheritance of disease seems to be an impossi- 

 biHty, for if the parasite enters the germ cell it is prac- 

 tically sure to destroy it, and there will be no progeny. 

 In many cases, however, progeny are born diseased, 

 but this is due to reinfection of the young embryo from 

 the body of the mother. This is not an inheritance but 

 a reinfection. In smuts, for example, there is much 

 reinfection by means of the transmission of spores upon 

 seeds. This can in no sense be spoken of as inheritance. 



In one respect, however, one may speak of disease 

 inheritance. Breeding experiments have shown that 

 predisposition to disease and disease resistance, com- 

 monly called susceptibility and immimity, are inherited. 

 This means that it is of germinal origin, so that it does 

 not involve the inheritance of an acquired character. 

 On the other hand, as was stated, Bolley maintains 

 that disease resistance is built up imder the influence of 

 disease attack, increasing gradually through the genera- 

 tions. This would make it an acquired character and one 

 that is inherited. 



These are a few of the examples of so-called acquired 

 characters and the claims for and against them. Investi- 

 gation is not yet in a position to come to any definite 

 conclusion in reference to them. The bulk of available 

 evidence, however, seems to be against the inheritance 

 of acquired characters; but there are a number of 

 biological facts that seem difiicult to explain in any other 

 way. In animals the mechanism may seem to make the 



