214 Cytoplasm as Seat of Genetic Properties 



formalistic, because of the desire to endow genes with definite 

 specific properties which explain whatever is found. Furthermore, 

 such theories are completely unnecessary. A physiological point of 

 view relating genie actions, which in themselves are the same in all 

 the crosses, to differences in general physiological features present in 

 different cytoplasm seems more appealing and is definitely simpler. We 

 shall see below that Stern himself has become skeptical about his 

 theory of genie action. Thus I conclude that there are no plasmon- 

 sensitive genes. Any genie material may act differently if the cytoplasm 

 does not provide the proper substrate tuned to the thresholds, veloci- 

 ties, and so on, of the reactions involved. It is gratifying to see that 

 Oehlkers (1952a), in a clear discussion of all these problems, has 

 come, at least in principle, to very similar conclusions, opposing the 

 idea of plasmon-sensitive genes, as the quotations above show. 



It is rather interesting that in Epilobium (just as in Lymantria) 

 indications of paternal effects have been found. (The same is true 

 of the OenotJiera crosses.) Michaelis found that in the course of his 

 matroclinous backcrosses some paternal effects appeared, shifting 

 the cytoplasmic action somewhat toward the normal side. We think 

 at once of cytoplasm introduced by the pollen and adding up in 

 the course of generations to a kind of dilution of the maternal cyto- 

 plasm, though Michaelis is not friendly to this idea. 



c. Evidence from merogony 



Since the classic work of Boveri and Godlevski, experiments on 

 merogony have played an important role in experimental embryology. 

 Merogony — the development of an enucleated egg fragment fertilized 

 by foreign sperm — should yield information on the relative roles 

 of nuclear and cytoplasmic heredity (recent review by von Ubisch, 

 1954). In repeating Boveri's experiments, Hoerstadius (1936) found 

 that reciprocal merogons of sea urchin species show differences in 

 regard to the skeleton. The details do not indicate any cytoplasmic 

 inheritance, but can be referred to ooplasmic predetermination and 

 the well-known fact that the nucleus plays only an inferior role 

 during the first stages of development, up to gastrulation. This may 

 be regarded as certain in view of the fact that these haploid merogons 

 do not develop very far, and die when normal genie action sets in. 

 Using a clever method of producing merogonic mosaics from am- 

 phibian eggs, Baltzer (1933) and Hadorn (1936) again found some 

 cytoplasmic effect, which, however, does not prove cytoplasmic in- 

 heritance proper, and parallels the sea urchin case in fact and 



