CYTOPLASMIC INHERITANCE 27-4 



After an interval of one month the experiments were continued 

 and more hybrids of the same group were tested. All showed less 

 activity than those which had been tested previously, although the 

 standard control baker's yeast tested had not chanced significantly. 

 In eight tests of the standard baker's yeast, the Qqqo values ranged 

 from 158 to 454; however, six of the determinations fell between 

 310 and 375. Fifty-nine of the hybrids had Qcqo''^ ^^ ^^°™ 218 to 

 744. The mode was around 475. Two of the hybrids had R. Q.'s of 

 1 with Qqoo'^ °^ ^ ^"^ ^^'^' ^^ ^^ clear, therefore, that cultures 

 stored for more than four months after the matings were made lost 

 a great deal of the heterosis that characterized the freshly-made 

 hybrids. In one instance, 9 cultures were isolated from the same 

 tube, a single isolate of which had previously shown a Q^Oo °^ 7900. 

 Eight cultures gave Q^nn's of from 403 to 534; one gave a q2.q of 

 64 with an R. Q. of 1. "^ ^ 



A clone originating from a single ascospore is a mixture of hap- 

 loid cells. I have pointed out that when hybrids between genetically 

 marked parents are made no new mutations are found in the hybrids 

 that could be interpreted as the result of mutations in the haplophase. 

 However, in terms of the fermentative ability of freshly made hy- 

 brids there were many differences between diploid hybrids from the 

 same tube. This suggests that there was a rapid diminution in vigor 

 occurring during the time of sampling. Sampling of these cultures 

 was not at random for only superior ones were selected for testing. 



Soon after hybridization the superior hybrids are about from 

 ten to twenty times more active metabolically than after they stabi- 

 lize at their standard level of activity. One culture tested on August 

 21 showed a Qpqo of '^^^^ ^^^ ^^ October the same culture showed 

 a Qqoo value of 480. Since these cultures were diploid and no sporu- 

 lationT)ccurred- their genotypes were presumably not altered over 

 this period. 



Several subsequent attempts were made to reproduce the above 

 experiments without success but the data are published because no 

 flaw has been detectable in the procedures that were employed and 

 the numerous controlled observations of high metabolic activity and 

 subsequent degeneration of the hybrids appears to be completely 

 authentic. Further experiments are being done from time to time in 

 an attempt to duplicate the phenomenon. 



THE EFFECT OF NUCLEAR DIVISION 

 WITHOUT CYTOPLASMIC DIVISION 



Winge and Laustsen (1940) described a variation involving change 

 of phenotype without apparent change in genotype. It occurred in the 

 course of inbreeding a culture during which changes in genetic com- 



