FIFTEEN- AND SIXTEEN- CHROMOSOME OENOTHERA MUTANTS IO7 
branching habits, etc. If this mutant bore signs of abnormality or 
irregularity such as were observed in the other two forms, the fact was 
not observed; yet the indications of abnormality in Nos. 3474 and 
5414 lead us to conclude that the gametic combination or combinations 
which produced these two plants may have been less "compatible" 
than the combination which produces 0. lata. 
Summary 
1. The primary object of this series of three reports, of which the 
one in hand is the second, is to discuss, in the light of the Cold Spring 
Harbor and Louvain studies of Oenothera, certain theories and con- 
clusions which Gates has advanced from time to time and which Gates 
and Miss Thomas have based upon the results of their investigations. 
2. 0. Lamarckiana mut. lata, long believed to have 14 chromosomes, 
is now known to have, invariably, 15. The researches of Gates and 
Miss Thomas appear to have led them to conclude, further, that the 
presence of the extra chromosome in the somatic cells of 15-chromo- 
some offspring of 14-chromosome forms is invariably associated with 
the presence of lata or lata-like vegetative characters. Later, Gates 
recognized the fact that his 15-chromosome mutant 0. incurvata is 
quite different from 0. lata, as is also a 15-chromosome form which 
de Vries reported. That he is loth to concede that these discoveries 
render untenable certain earlier statements of Gates and Miss Thomas 
is indicated by the statement that ''It is perhaps not inappropriate 
to speak of all these mutants as belonging to the lata series, or series 
with an extra chromosome." The primary object of this paper, 
therefore, is not only to emphasize the fact that these two mutants 
cannot be regarded as lata-like forms, but to show that many other 
15-chromosome mutant offspring of 14- and 15-chromosome forms, 
are not lata-Vike. 
3. The distinct types of mutants which the Cold Spring Harbor 
and Louvain studies have shown to have 15 chromosomes, are: (i) 
0. lata, (2) 0. alhida, (3) 0. bipartita, (4) type 5509 (supposed to be 
modified 0. ohlonga) — all Lamarckiana mutants. (5) 0. nanella lata, 
produced by 0. Lamarckiana, 0. nanella, 0. lata X 0. Lamarckiana, 
etc. (6) 0. suhovata, found in cultures of 0. Lamarckiana and 0. lata 
X 0. Lamarckiana. (7) A dwarf type, 2256, produced by 0. nanella, 
selfed. (8) Type 4499, found in cultures of 0. lata X 0. Lamarckiana 
and 0. lata, selfed. (9) 0. exilis, (10) 0. exundans and (11) type 
