DAUERMODIFI CATION 



pressive of its normal alternative And in addition it must be carried 

 by pollen as well as by eggs : it is amhiliiiear. 



In one variety of rogue pea a difference shows itself between 

 reciprocal F^'s in the early stages of growth. In both crosses some 

 of the plants begin, not as fuU rogues, but as intermediates. When 

 the rogue character has been carried by the pollen there are more 

 intermediates; the rogue effect is diluted and the dilution, as we 

 might expect, is greater in the male contribution. Now, the inter- 

 mediates turn into full rogues as they grow up, but the intermediate 

 parts bear flowers which can be bred from. The progeny of these 

 flowers includes both rogues and types and the proportion of rogues 

 varies : it is correlated with the degree of expression of the rogue 

 character at the node where the flower was borne. Thus the genetic 

 properties of the plant must change and develop with its external 

 character. For the first time we see heredity, unstable heredity, going 

 hand in hand with differentiation, abnormal differentiation. 



Dauermodification 



Since the plasmagene system depends on a chemical equilibrium 

 and is sometimes unstable in development it should be possible to 

 change it by special chemical or physical treatments during develop- 

 ment. Such treatments, inaugurated by Jollos, have in fact been 

 successful in producing what he called Dauermodifications, changes 

 in cytoplasmic heredity: with protista such as Paramecium, arsenious 

 acid and heat shocks were used, with Phaseoliis chloral hydrate, and 

 with Drosophila merely high temperatures. 



These changes are inherited in the female line but, even with 

 selection of the individuals most strongly affected in each generation, 

 the changed type has always hitherto been found to disappear, after 

 a few sexual generations {see Table 17). The mutant plasmagene 

 has not the hereditary staying power of the natural ones we have 

 considered. Does this imply that it falls into another and inferior 

 category? Probably not. These new effects are usually deleterious, 

 at least when the determining conditions have been removed. This 

 means that the conditions of chemical equilibrium governing the 

 new plasmagene will favour its disappearance. And since it can 

 scarcely be indispensable to the cell, those cells which have lost it 



183 



