256 A - B - Stout Cytokgia 3 



and that they possess in common at least some of the same hereditary- 

 factors for incompatibility. 



Thus far no seedling has been obtained from the numerous self- 

 and cross-pollinations involving only these triploids. There is much 

 abortion of pollen in these triploids but there appears to be complete 

 self- and cross-incompatibility for those spores and gametes which are 

 functional— a type of sterility very common in daylilies. Offspring 

 have been obtained by crossing triploids with certain diploids, and 

 chromosome counts have been made for 44 of these seedlings. The 

 majority of these seedlings are diploids, a few are triploids, and several 

 are aneuploids with somatic numbers that are fluctuating for various 

 numbers between the diploid and the triploid. In several plants there 

 are individual cells with higher than the triploid number or with lower 

 than the diploid number but no plant seems to be reasonably uniform 

 for such a number. Thus in one plant counts of 12, 15, 22 and 23 seem 

 valid but the lower numbers are not sufficiently frequent to admit of a 

 decision that the plant is, or ever was, fundamentally a para-haploid or 

 a sub-diploid. 



From the chromosomal complex of the seedlings of triploid- diploid 

 parentage it seems clear that for the triploids the chromosome number 

 in the spores and gametes which mature and function is most fre- 

 quently 11, that a few of the gametes may have 22, and also that 

 various numbers between 11 and 22 may be present in functional 

 spores. The cytological evidence for the triploid Europa Daylily clearly 

 shows that abortion during sporogenesis eliminates many nuclei and 

 especially those with few chromosomes, but it is certain that spores 

 with as few as six chromosomes (Stout and Susa, 1929) may develop at 

 least to the stage of the division of the primary cell. It may perhaps 

 be assumed that gametes with less than 11 and with more than 22 

 chromosomes may sometimes mature and be functional. 



The existence of self- and cross-incompatibility in these triploid 

 daylilies greatly limits the chance of obtaining offspring from the fusion 

 of two gametes both of which have higher than, or less than, the set of 

 11 chromosomes. As long as the seedlings obtained have one parent 

 which is diploid there is little chance of advancing to higher levels 

 of polyploidy. Attempts will now be made to obtain seedlings between 

 triploids by utilizing the new seedlings that are triploids or para- 

 triploids. It is obvious that pollen abortion and incompatibility in 

 fertilization have operated to restrict and prevent the further extension 

 of polyploidy in the long period of time during which the older triploid 



