FIFTEEN- AND SIXTEEN-CHROMOSOME OENOTHERA MUTANTS 69 
both sides of the left distal of 2, the latter, as it grows, being crumpled 
into the slit thus produced by 4. Stripping back the sepals of a bud 
about to flower, one will find the two petals locked in this manner, 
the a lobe of 4 overlapping the a' of 2, and the h' lobe of 2 overlapping 
the h of 4.^^ When the flower unfolds, petal 4 may be found with a 
diagonal slit extending from about the middle of the right half of the 
distal margin towards the median line of the petal. Petal 2 may or 
may not have a slit extending from about the middle of the left distal 
margin towards the median line. It is usually present, and shorter 
than the slit in petal 4. In the case of the flower shown in Fig. 6, 
petal 2 has the longer incision, indicating that lobe a' of petal 2 over- 
lapped lobe a of petal 4, and that lobe 6 of 4 overlapped b' of 2. 
Flowers are found with one, two, three, or all four, of the petals cleft. 
Sometimes a petal has two slits, one on each side of the median line. 
In an irregularity such as that first described above, the right margin 
of I, as well as the left of 3, is in, consequently these two sometimes 
mterfere, causing an incision either in the left distal margin of 3, or the 
right distal of i, or both. Sometimes petal i, both margins of which 
are in, wraps around the filaments and anthers. The right and left 
distal margins may then come in contact in such a way as to cause the 
two incisions sometimes found in a petal. Not infrequently an ir- 
regularity in petal arrangement causes no cleavage. Although cleft 
petals are sometimes produced by overhanging anthers, in the majority 
of cases they result from interferences caused by a partial reversal 
of the direction in which the petals are normally rolled within the bud. 
0. hipartita is distinguished by the large number of flowers produced 
with cleft petals. Flowers with cleft petals are found occasionally on 
individuals of almost any type, including Lamarckiana, but they are 
more common to hipartita than any other mutant type observed. 
The petal whose base is attached at the point where the filaments separate is 
designated as petal 1. 
The first flowers of vigorous rosette and stem branches (probably also of the 
stem) appear to be more subject to this irregularity than those produced by the same 
parts near the extremity. It is possible also that the first flowers of the short, weak 
secondary branches produced late in the flowering season are less subject to this 
irregularity than the first flowers of more vigorous parts, but the facts have not been 
ascertained regarding this point. The buds of two biennial Lamarckianas were 
examined daily (with occasional exceptions) throughout the greater part of the flower- 
ing season. Plant A came to flower June 23 and B about the same time. The former 
was examined for cleft-petaled flowers for the first time on June 29, and the latter 
on June 28. The results for these days and the 11 and 12 following, were recorded 
as follows: 
