FIFTEEN- AND SIXTEEN-CHROMOSOME OENOTHERA MUTANTS 6l 
writer that the authors' announcements were a bit premature in view 
of the fact that the somatic chromosome numbers of so many mutant 
offspring of 14-chromosome O. Lamarckiana had not been reported. 
For example, the somatic chromosome numbers of 0. scintillans, 
O. spathulata, O. elliptica, 0. sublinearis, 0. leptocarpa, 0. subovata, 
etc., all Lamarckiana mutants, had not been announced at that time. 
The same is true of 0. nanella lata,^^ 0. nanella ohlonga and 0. nanella 
elliptica — compound types appearing in 14-chromosome 0. nanella 
cultures and elsewhere. Furthermore, as previously stated, it has 
been shown (1908) that 0. albida, one of the very common Lamarckiana 
mutants, is a 15-chromosome form, yet this plant cannot be listed 
either as 0. lata or as a lata-llke form. 
I have studied the somatic chromosomes of 305 plants of the 
Lamarckiana group and have determined the precise number of 234 
individuals. Exclusive of the two 14+^-chromosome mutant types 
mentioned in the preceding report, of the offspring of O. lata X 0. gigas, 
O. Lamarckiana X 0. gigas, 0. nanella X 0. gigas and of 0. gigas, 
selfed, 16 distinct mutant types were found among these 2^4 individuals 
(j/ among the 30s) having more than 14 chromosomes; 11 of the 16 were 
i^-chromosome forms, j were 16- and 2 were triploid. The i/th type 
having 14 -f- chromosomes was also a triploid form. In addition to the 
above, one type having a number of characters in common with one 
of the eleven 15-chromosome types mentioned, was also found to 
have 15 chromosomes. Also, 15 chromosomes were repeatedly counted 
in root- tips from a mutant grown at Amsterdam in 1 91 2 and identified 
by Professor de Vries as 0. oblonga, but a certain irregularity found in 
several tips of the plant (to be described later) indicated a possible 
abnormal condition and made it seem inadvisable to accept the count 
in this individual as typical of the species until verified by counts in 
other oblongas.^^ Besides the 11 or 12 types which were ascertained, 
12 Hunger ('13) found plants which he identified as 0. lata nanella and O. ohlon- 
ga nanella in cultures ol 0. Lamarckiana. 
^3 I have since verified this count in 13 additional albida mutants. 
Professor de Vries has kindly aided me in every way to determine the precise 
number of chromosomes in the Amsterdam type. In the early summer of 1915 he 
sent me a number of young ohlonga rosettes from his gardens, but, unfortunately, all 
perished before reaching their destination. He also sent me a generous supply of 
seeds from one of his best plants, but very few of these germinated and only one 
seedling survived. Root-tip fixations were prepared from this plant, but no satis- 
factory counts have been obtained from them thus far. 
