OENOTHERA MUTANTS WITH DIMINUTIVE CHROMOSOMES 513 
day near the height of the flowering season. The petals were smooth 
and a sHghtly Hghter yellow than is characteristic of O. Lamar ckiana. 
A portion of the buds produced a moderate abundance of pollen con- 
taining relatively few seemingly good grains and still others none at 
all. It was almost impossible to obtain seed from the self-pollination 
of this form. 
The somatic chromosomes of the 1908 mutant (No. 3878) were 
studied and the number determined in the autumn of 1909. Finding 
that this plant had 14 chromosomes of the usual size and i small one, 
it was recalled that a second mutant (No. 4605) of the same type had 
been produced by 0. lata X O. Lamarckiana in the season which had 
just passed; therefore root-tips from this plant were sectioned and 
studied with much interest, and here also 14 chromosomes of the usual 
size and i small one were found (late autumn of 1909). 
Unfortunately, but one fixation of 16 tips had been prepared from 
No. 3878 and one of 20 tips from No. 4605. These were not wholly 
satisfactor\^ for study, as the fixations were poor and only compar- 
atively few figures were found in perfect metaphase (the only satis- 
factory stage for the determination of chromosome number in root 
tips of Oenothera) . However, the tendency of the small chromosome 
to occupy a peripheral position on the equatorial plate and to be alloted 
the full space of a lar^e chromosome, often made it possible to deter- 
mine the presence of the small member when it was impossible to 
count the long ones. 
In transverse sections of root-tips from No. 4605, 25 metaphase 
figures were observed, showing the small chromosome with un- 
mistakable clearness. In but 8 of this number were the large chro- 
mosomes sufficiently well separated to make it possible to count them 
accurately, but in each of the 8, 14+^ were clearly demonstrated 
(figs. 2 and 3). 
In- No. 3878, 59 figures were observed in which the small chro- 
mosome was clearly identified. In 30 of the 59 the chromosomes were 
sufficiently well separated to enable one to determine the number 
precisely, and in each of the 30, 14+^ were counted (fig. i). 
Although in both plants the small chromosome occupied a peri- 
pheral position on the equatorial plate in the majority of cases (figs, i 
and 3), its position was by no means constant, as it was found farther 
in occasionally (fig. 2). 
In 1911 and 1912 I had the privilege of preparing fixations for the 
