FIFTEEN- AND SIXTEEN-CHROMOSOME OENOTHERA MUTANTS 55 
bination of chromosomes received." He does not state, however, 
that these discoveries render untenable certain earlier conclusions of 
Gates and of Gates and Miss Thomas concerning the relation of the 
extra chromosome to lata and /a/a-like characters, but takes what 
appears to be a last brave stand to save the day in the statement which 
follows the words quoted above: ''It is perhaps not inappropriate to 
speak of all these mutants as belonging to the lata series, or the series 
with an extra chromosome." It must be conceded, however, that a 
plant which de Vries clearly states has none of the characters of 
0. lata, can not logically be held to belong to the lata series of mutants. 
Furthermore, it has been shown in the note which preceded this 
publication (Lutz, 'i6a) that a number of distinct mutant forms, quite 
unlike 0. lata, have been found by the writer to have 15 chromosomes. 
The chromosome number of each of the 9 un/a/a-like types reported 
was ascertained, and their dissimilarity to 0. lata fully recognized, 
previous to the year 19 13. 
The primary object of this paper, therefore, is to discuss Gates's 
and Gates and Miss Thomas's theories and conclusions regarding the 
extra chromosome at length in the light of the fact that many unlata- 
like 15-chromosome mutants are now known and that many more 
doubtless exist, in order that it may be shown that many of their 
conclusions are untenable. 
B. 15-CHROMOSOME Mutants 
1. Has O. lata 14 or Chromosomes? Is the Number of Somatic 
Chromosomes Inconstant in this Form? 
For a period of four or five years following the announcement of 
the somatic chromosome number of 0. Lamarckiana by Geerts in 
1907, all mutant offspring of 0. Lamarckiana, with the exception of 
0. gigas, were supposed to have the same number of chromosomes as 
the parental form; namely, fourteen. Fifteen chromosomes had been 
reported for 0. albida^ in one of the earlier notes published by the writer 
(Lutz, '08), but the discovery was not emphasized and doubtless was 
overlooked, with the result that 0. gigas continued to be regarded as 
the sole mutant derivative of 0. Lamarckiana with a chromosome 
number differing from that of the parental form. 
^ Two plants. Notwithstanding the fact that they were offspring of 0. lata 
X 0. Lamarckiana, they were mutants, since 0. alhida was not employed as either 
parent. 
