196 Cytoplasm as Seat of Genetic Properties 



difference in quantity of egg and sperm cytoplasm is obvious, and it is 

 safe to assume that the sperm usually does not bring any undif- 

 ferentiated cytoplasm into the egg, or at least not much of it. But this 

 is not true either for non-filiform sperm or for the plant "sperm." We 

 shall see that facts in favor of an action of sperm cytoplasm have 

 actually been found. 



Cytoplasmic inheritance could, however, be expected to occur on 

 a higher level than the one just discussed. This would mean that the 

 cytoplasm is not simply diversified as a substrate for genie action, but 

 by itself has a type of hereditary function which is comparable to that 

 of the genie material. This means that the cytoplasm as a whole, the 

 "plasmon" as von Wettstein called it, may determine, without any 

 nuclear interference, specific characters which then exhibit purely 

 matroclinous inheritance independent of whatever nucleus is present. 

 It is imaginable that all transitions exist, from a specific and inde- 

 pendent plasmon through many gradations of collaboration with 

 nuclear genie effects to the simple substratum action. The technique 

 for the study of such possibilities is of course the continued backcross 

 among the descendants of reciprocal crosses, thus replacing step by 

 step the proper nucleus by a foreign one in the respective opposite 

 cytoplasm. A large part of the work on so-called cytoplasmic heredity 

 deals with this problem. 



A specific type of plasmon action, meaning control of hereditary 

 traits independent of the nucleus, would be established if we could 

 locate visible or invisible self-duplicating structures which are re- 

 sponsible for definite, specific hereditary features. A number of 

 geneticists have used the term "plasmagenes" for these visible or in- 

 visible parts, and some of them speak of plasmagenes as an indis- 

 putable counterpart of the nuclear genes. I do not think that such an 

 attitude is justified as yet. I have considerable misgivings in regard to 

 the terminology. Though this is a minor point, terminology has a 

 tendency to be suggestive of ideas which may be completely wrong. 

 I do not want to point out that the idea of the gene itself is becoming 

 rather shaky, though we might use the classic term simply for the 

 sake of convenience without going into the details of its meaning. But 

 the gene, or genie material as I prefer to say, is historically so com- 

 pletely linked with the chromosome and Mendelian inheritance that it 

 can only produce confusion if any self-duplicating body or substance 

 is called a gene. Certainly, self-duplication is a prominent feature of 

 the genie material in the chromosomes, but it is not the totality of its 

 properties. If we call all self-duplicating particles genes, we give up 



