46 T O R R E Y A 



classes of its pollen. Also two plants of the same genotype are cross- 

 incompatible. When two plants possess one factor in common (AA 4~ 

 $i ^2 X AA — S 1 5*3 i there is incompatible elimination of fertilization 

 for the pollen which carries that factor. But when there is no common S 

 factor f AA — S 1 S-2 X AA — So 5 4 ) there is no incompatible reaction and 

 the two individuals cooperate fully in reproduction as do any two members of a 

 species or group that possesses no incompatibility factors. In the 23 plants 

 grown from seed from Argentina there were 12 different genotypes of from 

 one to three individuals for which there was inter-genotypic cross-repro- 

 duction. 



Auto-tetraploids of Petunia axillaris and their Intra-group 

 Reproduction 



Induced auto-tetraploids were readily obtained by spraying buds of young 

 seedlings of diploid | 2n = 14) P. axillaris with solutions containing colchi- 

 cine. From one to three lateral branches which were 4n were obtained on 

 fifteen different seedlings which were otherwise 2n. These seedlings were of 

 several genotypes in regard to S factors. 



There was complete inhibition of the reaction of self-incompatibilities in 

 the flowers of all 4n branches. The self-pollinated flowers of 4n branches 

 produced large capsules well filled with man}" viable seeds while the flowers 

 of diploid branches remained fully self-incompatible. (See figure 1. I 



This inactivation of incompatibility factors was inherited in seedling off- 

 spring. Seed progenies of selfed flowers of 4n branches were grown for six 

 different plants and the total of such seedlings was 212. Another seed genera- 

 tion, the second for the generations of induced tetraploids. totaling 86 in- 

 dividuals, is now in heavy bloom. Every plant of these progenies was tetra- 

 ploid. Every seedling produced large capsules and many viable seeds to normal 

 self-pollination. Several thousand of the cross-relations between tetraploid 

 plants Gntra-series. inter-series. 4n parents and 4-n progeny, etc. i were 

 tested by controlled pollination;.. Everv one of these intra-tetraploid cross-rela- 

 tions resulted in capsules and many viable seeds. 



Evidently in these tetraploids only microspores and macrospores which 

 possess two genomes function in the intra-group fertilizations and seed repro- 

 duction. Thus the inactivation of self- and cross-incompatibilities which arose 

 as a discontinuous condition in induced 4-n branches is hereditarv on the selfed 

 offspring, which have also been 4n. 



Inter-Group Relations between the 2n and the 4n Groups of Petunia 



axillaris 



In the report of 1942 i 9 I it was stated that in the reactions of fertilization 

 the tetraploid X diploid relation for the tests made entirely failed to produce 



