T. M. SONNEBORN 209 



second choice method of fertilization, which is required to fore- 

 stall clonal death, takes a form in which inbreeding is less in- 

 tense. There is no published evidence to decide with assurance 

 whether immaturity follows old-age selfing, but Giese's (1957) 

 comment about obtaining a series of successive inbreedings in 

 variety 16 following selfing suggests that immaturity after this 

 sort of conjugation may be lacking as it is after autogamy. If so, 

 this would permit rapid restoration of the heterozygosity lost by 

 selfing. The episode of selfing would thus serve to rejuvenate 

 and give more time for crossing without sacrificing heterozy- 

 gosity. 



The contrast between these two inbreeding and two outbreed- 

 ing varieties illustrates how differences in some of the major 

 life processes bear on the breeding system. The same features, 

 with mainly quantitative differences, and some additional ones, 

 are encountered in the other varieties, as will now appear. 



3. Variety 12. Very little is yet known about the only avail- 

 able strain of this variety. It has an immature period of unde- 

 termined length and a long mature period that probably extends 

 for more than 80 fissions. Yet its fertilization process during 

 senility is autogamy. Thus it seems to be a somewhat less extreme 

 outbreeder than varieties 15 and 16. 



4. Varieties 1, 2, 3, 7, 9, and 11. These varieties are all less 

 extreme outbreeders than varieties 12, 15, and 16, and less ex- 

 treme inbreeders than varieties 10, 14, and those to be discussed 

 later. However, not enough is yet known about them to rank 

 them in a definite order. Little is known about variety 11, of 

 which only two strains have been found. It belongs to group A, 

 has a moderately short period of maturity, and undergoes autog- 

 amy. Immaturity has not been studied in it; but the relatively 

 short total interval until senility begins precludes any but a 

 very short immaturity. Variety 11 could not be a strong out- 

 breeder. Variety 7 has long been known only as a single strain 

 pure for mating type XIII. Recently a few more strains have 

 been found. These are not pure for mating type, but show the 

 group A method of mating type determination. All come from 

 Florida. Preliminary observations indicate no immaturity and 



