FIFTEEN- AND SIXTEEN-CHROMOSOME OENOTHERA MUTANTS 59 
"about" 14 chromosomes, but that the number for 0. lata has since 
been shown by Lutz, Gates, and Gates and Miss Thomas, to be 15. 
These facts are outHned at length in order that the reader may 
understand that mistaken identification of one plant by Lutz and 
possible mistaken identification or error in count by Gates are 
responsible for the early statement that 0. lata had 14 chromosomes. 
It may be assumed with safety now that the number of somatic chro- 
mosomes present in the type of 0. lata produced by 0. Lamarckiana 
is invariably 15. 
2. O. lata and the "Extra'' Chromosome 
In "Recent papers on Oenothera mutations" Gates ('13, pp. 301- 
302), as stated above, mentions the then unpublished results of in- 
vestigations conducted by Gates and Miss Thomas ('14) which had 
disclosed 15 chromosomes in 21 plants classified by them as 0. mut. 
lata, 0. mut. semilata, 0. lata to semilata, 0. mut. lata rubricalyx, 
0. biennis mut. lata and as lata-Yike forms. Referring to O. lata 
rubricalyx which appeared among the F2 offspring of two 14-chromo- 
some forms crossed (0. rubricalyx X 0. grandiflora), he says: "The 
possession of fifteen chromosomes by this plant also shows that 
whenever a meiotic irregularity leads to the formation of an individual 
having an extra chromosome, such a plant will have the leaves and 
habit of lata or semilata.'' Although he adds in a footnote that "It 
is possible that one or two other mutants also have an extra chromo- 
some," he does not state or intimate that such forms are not lata-Vike; 
furthermore, Gates and Miss Thomas say in the later report (pp. 551- 
552), "Certain other mutants indicate by their hereditary behaviour 
that they may also have aberrant chromosome numbers, but this has 
not yet been proved, except in gigas." 
Gates was the first to show that one of the heterotypic chromosomes 
of a form may pass "into the same daughter-nucleus as its mate, instead 
of into the opposite nucleus." He first demonstrated this significant 
irregularity in 14-chromosome Lamarckiana in 1907, but has since 
observed the same peculiarity in many other forms. With reference 
to this occasional 6-8 distribution of heterotypic chromosomes in 14- 
chromosome forms, Gates and Miss Thomas say (p. 550) : "Whenever 
this irregular meoitic division occurs in a pollen mother-cell, such a 
cell will, at least in many cases, give rise to two /a^a-producing pollen 
grains in addition to two having only 6 chromosomes. The latter 
