48 TORREYA 



barrier extends to all 2n and 4n genotypes of the entire species is, of course, 

 not determined and there is some evidence that it may not do so when dis- 

 tinctly different genotypes are involved. 



The Status of Spore Abortions in Hybridity and Autopolyploidy 



An adequate review of the several distinctly different types of sterility which 

 operate in amphiploidy and autoploidy is not possible at this time. It should be 

 noted that much attention has been given to the fact that when branches or 

 seedlings of ''sterile'' ¥ 1 hybrids become tetraploid the flowers of such amphi- 

 ploids may be highly "fertile." But in these cases the sterility involves abortion 

 of spores and pertains to the total potential ability of individuals to function 

 in any relation in seed reproduction. This is entirely distinct from the intra- 

 specific (or intra-group) self- and cross-incompatibilities and also from the 

 inter-specific barriers to hybridizing fertilizations. But abortion of spores and 

 abortion of seeds may be features either (a) of inter-specific barriers which 

 operate after successful fertilization has produced a hybrid progeny, or (b) of 

 the irregularities of sporogenesis in both F 1 hybrids and pure autoploids. 



Inter-specificity for 2n and 4n Populations when there are no 



I NTRA-I N COM PATIBILITIES 



That there may be the operation of a sterility barrier between closely related 

 2n and 4n populations in various cases in which there are no self- and cross-in- 

 compatibilities has been well established. Miintzing in 1936 (3) presented an 

 extensive survey of the data on this matter and concluded that a purely quan- 

 titative chromosome doubling often results in structural and physiological 

 changes in specificity and that different chromosome races of a single species, 

 including experimental autoploids, are generally separated from each other by 

 barriers of "incompatibility and sterility." But Miintzing uses the term "incom- 

 patibility" for the inter-relations between entire species or groups of individuals 

 and he does not mention any behavior of intra self- and cross-incompatibili- 

 ties though they are known in some of the 2n species which he surveys. It 

 must be stated and perhaps emphasized that self- and cross-incompatibilities 

 are not necessarily absent or inactive in tetraploid species. Among well estab- 

 lished natural species they may be present or absent either in species of low 

 chromosome number or in species that are evidently polyploid, even in the 

 same genus. 



Data for Experimental Auto-tetraploids Derived from 2n Plants 



WHICH HAVE INCOMPATIBILITY FACTORS 



There are somewhat meagre data on the behavior of incompatibilities in 

 autotetraploids definitely known to have arisen from diploids in which self- 



