The Cytoplasm as Specific Substrate 213 



ser (1935), who found plasmon actions on growth in crosses of wild 

 tomatoes, thinks that the decisive features are osmotic conditions. 

 The genically controlled growth requires an optimum osmotic pres- 

 sure, while definite osmotic values are controlled in the cytoplasm 

 and may be inadequate when the wrong cytoplasm is present. This 

 may be expressed also in terms of thresholds. Von Dellingshausen 

 (1935, 1936) tried to find the physiological conditions responsible for 

 plasmon effects in Michaelis' Epilohium crosses. He found differences 

 in permeability and viscosity, that is, physical differences. Lehmann 

 and his students (Ross, 1940) found deficiencies in heteroauxins in 

 the plasmons which inhibited growth, and could overcome the effect 

 by treatment with auxins. More important still is Ross's (1941) find- 

 ing that peroxidase activity in the foreign plasmon is higher than 

 in the proper one. All the different effects of growth inhibition in 

 the hybrids with foreign plasmon may be traced to this primary 

 difference. These results tend to point in the same direction as our 

 foregoing analysis, and to show that in a general way the interpre- 

 tations adopted above are correct and preferable to the ideas on 

 genie cytoplasm or cytoplasmic genes. 



I prefer a statement of the facts in terms of generalized bio- 

 chemical features of the cytoplasm, like respiratory enzyme levels, 

 which either allow genically controlled reactions with the substrate 

 to occur within the normal threshold limits or prevent them. Explana- 

 tions in terms of plasmon-sensitive genes certainly account for the 

 same facts, but, I think, only in a formalistic way. To mention only 

 one such theory, Caspari has elaborated the idea, based upon Stern's 

 hypothesis of genie action (to be discussed later), that each allele 

 has a characteristic combining power with the substrate, the genie 

 product being the result of this combination with the substrate for 

 which different genes compete. As the amount of substrate is limited, 

 the final result will depend upon the outcome of the competition 

 among different alleles. It is assumed that the substrate produced 

 in the cytoplasm of different strains is somewhat different; further, 

 that the foreign gene has a higher combining power but a lower 

 efficiency toward this particular substrate, and transforms it into a 

 physiologically inactive product. In the hybrid the foreign allele takes 

 the substrate away from the rightful one, which thus cannot produce 

 enough product. This would be the essential feature of a "plasmon- 

 sensitive gene." 



I have the feeling that this and similar ways of looking at the 

 facts from the point of view of different types of genes are rather 



