162 



with the shelled rhizopod Difflugia, states that most of the work on uni- 

 parental reproduction has yielded the result that during such reproduction 

 the hereditary constitution (genotype) appears not to change though the 

 organism may differ much in outward character. Many papers cited 

 support this view though some are opposed. Jennings sayeTwiIirregard to 

 his own results: "After many generations of descent from a single progenitor, 

 such a single family .... has differentiated into many he- 

 reditarily diverse stocks." These diverse stocks differ hereditarily not only 

 with respect to particular single characters but also with respect to the 

 combination of characters. Many individuals of uniparental reproduc- 

 tion have shown a marked permanence of hereditary character in single 

 lines of descent, all the progeny being like the parent in hereditary consti- 

 tution; and further, many such lines, diverse in hereditary constitution may 

 exist in a population, and the effects of selection consist mainly, if not 

 entirely, in the isolation of such diverse lines. 



East sees no reason to believe bud variation different from germinal 

 mutation and says that it may be progressive, digressive, or retrogressive. 

 Bateson (10) holds that bud variations are due to qualitative cell-division 

 in somatic tissues, giving somatic segregation of unit factors. East points 

 out that in the large majority of cases of bud variation there has been 

 simply the loss of a dominant character and hence the appearance of a re- 

 lated recessive character. In some cases there is absolute disappearance 

 of the dominant character; in other cases it appears to be latent, and it may 

 reappear. Variations in color constitute over 70% of all bud variation. 

 Colony color in Helminthosporium is also a very common variable but 

 this is, in all probability, entirely incomparable with color variation in 

 flowering plants. 



Brierley (28) holds, for Botrytis, that even if sexuality occurs, the 

 fungus is "on all evidential criteria, an asexual homozygotic organism in 

 which the isolation of a single spore strain necessarily implies the isolation 



of a 'pure line' " A genotypic change in a pure line is a 



mutation." Similarly, Shear and Wood (105) regard individuals orig- 

 inating from single spores of Glomerella as homozygous, though on reason- 

 ing differing somewhat from that of Brierley. Crabill (36) also holds that 

 since his fungus "reproduces asexually segregation from heterozygous 

 parents cannot explain the origin of the strains." Accepting Brierley 's 

 criteria, my Helminthosporium single-spore isolations are equally homo- 

 zygotic. In at least three forms on cereals Helminthosporium is known 

 to be the conidial stage of the ascigerous genus Pleospora. As ascigerous 



