SUPPRESSIVENESS AND AMBILINE ARITY 



merely to the negative aspect of suppressiveness already seen in 

 Paramecium. In one stage of development it may fall as far behind 

 the average rate of multiplication of their cells as, in another stage, 

 it is in advance of it. And once it is sorted out and omitted from 

 a cell, that cell and its posterity will be free of it. 



Summing up: teclinically we recognize cytoplasmic heredity by 

 its non-mendelian habits. Alternative conditions are found, but they 

 are not alternatively inlierited in the sense that their determinants 

 are subject to segregation at meiosis. Further, their transmission is 

 not equally by egg and sperm, but as a rule bears some relation to 

 the volume of cytoplasm contributed. They are either matrilinear 

 or ambilinear. A determinant that succeeds in being carried effec- 

 tively by way of the pollen does so by virtue of being suppressive 

 of its alternative." Plastogenes obey the rules of plastid distribution: 

 they are carried by the pollen in some plants and not in others. 

 Plasmagenes, on the other hand, vary in effect in the same individual, 

 that is to say, in their concentration in the cell during development. 

 And when in low concentration, plasmagenes (like the plastids) are 

 liable to uneven sorting out and consequent somatic segregation. 

 At higher concentrations they are subject to the chemical equilibrium 

 of the cell, an equihbrium imposed by the total reactions of genotype 

 and environment. 



It follows from these conditions that plasmagenes must be much 

 easier to distinguish in one-celled organisms, whose environment 

 can be changed experimentally than in the higher organisms, where 

 the tissue is the invariable substrate o£ the cell. What we call 

 plasmagenes in micro-organisms must have chemical counterparts 

 in the cells of higher organisms. The reproduction of these counter- 

 parts must be under the control of the whole organism during 

 development, and they themselves must be concerned in determining 

 the processes distinguishing one kind of cell from another. The 

 parts played by the cytoplasm and the nucleus must be different in 

 development just as they are in heredity. What those parts are 

 we must now examine. 



REFERENCES 



ANDERSSON-KOTTO, I. 1930. Variegation in three species of fems. Z.I.A.V., 

 56: I 17-201. 



187 



