STOUT: INACTIVATION OF INCOMPATIBILITIES 49 



and cross-incompatibilities operate? Often the data given are confined to "Self- 

 sterility" and are indefinite, incomplete and to some extent inaccurate in this 

 matter. Especially is this the case for the petunias. 



Lewis and Modlibowska (8) consider that certain tetraploid "systematic 

 species" (possibly some are clones) that are "self-compatible" may have 

 arisen from 2n "self-sterile" plants of Allium, Tulipa, Hyacinthus and Prunns. 



Of the more reliable data for experimental autotetraploids there is one 

 statement (8) that self-incompatibility continues to operate in derived seed- 

 ling autotetraploids of Oenothera organensis, and a report (10) with data that 

 both self- and cross-incompatibilities operate in a tetraploid seed progeny de- 

 rived experimentally from 2n plants of Oenothera rhombipetala Bridgeport. 



There is one case reported which corresponds, in part at least, to the rela- 

 tionships here presented for the diploid and the autotetraploid Petunia axillaris. 

 The 2n clone of the cultivated pear, Fertility, has been described as "only 

 slightly self- fertile" (5) and as able to produce a good crop of seedless parthe- 

 nocarpic fruits (7). A 4n clone named "Improved Fertility" that arose as a 

 somatic bud-sport from Fertility was found to be definitely "more self-fertile" 

 than the 2n type (5, 7), able to set a full crop of fruit and seed to its own 

 pollen, and "fully self-compatible" (8). For the inter-relations in reproduction, 

 the 4n clone Improved Fertility X the 2n clone produced no fruits (45 flowers 

 were pollinated) but for the 2n clone X the 4n clone "a full set of fruits and 

 seeds is obtained" (7, 8). 



The intra-clonal and the inter-clonal relations in fertilization of the 2n 

 pear, Fertility, and its 4n bud-sport seem to be like those of the 2n and 4n 

 branches of each of the 15 original plants of Petunia axillaris which were 

 treated with colchicine. But further similarities are not so evident. In Petunia 

 axillaris the seeds of 2n X 4n are not, it now appears, viable ; in the cultivated 

 pears the seeds derived from 2n X 4n (see text — figure 1 and table 3 of 7) 

 are, it seems, highly viable. The 4n Improved Fertility X five diploid clones 

 other than Fertility was highly fertile in terms of fruit and seed production to 

 two clones, much less so as to two other clones, and fruitless to one clone. The 

 clones of pears correspond to individual seedlings of a species which may differ 

 in genotypic constitution. 



Diversity in Constitution 



Much remains to be learned regarding the diversity in the behavior of self- 

 and cross-incompatibilities in experimentally produced tetraploids. Incom- 

 patibilities both self and cross are extremely diverse in character, expression, 

 and genetical nature (4). Uniform results can not be expected for all the di- 

 verse types especially when the simpler "personate type" is compared with 

 the complex associate type, and when amphiploidy is involved. It is well es- 

 tablished (4) that some of both the diploid and polyploid hybrid cultivated 



