SUPPRESSIVENESS AND AMBILINEARITY 



as phenocopies. These, of course, differ from dauermodifications in 

 not being heritable. 



TABLE 17 



DECAY OF THE DAUERMODIFICATION OF PHASEOLUS 

 VULGARIS AFTER TREATMENT WITH 0-75 PER CENT 

 CHLORAL HYDRATE: 200 PLANTS IN EACH 

 GENERATION, SELECTED FROM THE MOST AB- 

 NORMAL INDIVIDUALS (HOFFMANN, 1927) 



Suppress'weness and Amhilinearity 



The working of the plasmagene system now begins to take shape. 

 Intermediates show dilution and, in so doing, show that the system 

 is divisible. There must be a number, a varying number, of like 

 plasmagenes in each cell of the multicellular, as well as of the 

 unicellular, organism. This number changes with development and 

 its change appears as suppressiveness. The action of suppressiveness 

 is revealed also in the origin of rogues. In one variety, where it 

 happens that the mutation occurs later or more slowly than in others, 

 the young rogue plants begin as intermediates. Evidently the rogue 

 plasmagenes have not established themselves and reached equilibrium 

 in the seedling. In crosses, provided that a necessary minimum 

 number are carried over by the pollen, and in new rogues, provided 

 that mutation is early enough, suppressiveness will ensure that the 

 plant will ultimately be a rogue just as Killer admixture swamps 

 non-Killer in Paramecium. The rate at which a plant becomes a rogue 

 is a measure of suppressiveness. Thus suppressiveness implies 

 amhilinearity even where, as with plasmagenes, inheritance carmot 

 be equilinear. And if there were varieties having a nuclear genotype 

 in whose company rogue plasmagenes were not suppressive, the 

 change to rogue would never come about in them and the rogue 

 mutation would never appear. 



i85 



