Studies on the Variability and Heritability of Pigmentation in Oenothera. 355 
the wider the region “irrigated” on either side of the median ridge. 
It is probable that there is some substance necessary to anthocyan 
production (perhaps tannins or certain enzymes) present in the sepal 
cells in O. rubrinervis, which is not present in the cells of the median 
ridge, for even when the color of the pattern is fully developed 
(plate VI, fig. 7) the median ridge remains green. In O. rubricalyx 
however (plate VI, fig. 8) there is such an abundance of the materials 
for anthocyan production that the whole sepal and hypanthium and 
the median ridge as well is flooded with it. 
II. Inheritance of pigmentation in Oenothera, 
The data presented in the preceding section indicate that, in 
O. rubrinervis as well as in several other mutants, within the ordinary 
range of variability, degrees of pigmentation are not inherited. Buds 
of the race known as No. 25, however, treated as a population, show 
in the aggregate a somewhat greater amount of pigmentation than 
does a population of O. rubrinervis buds grown under the same con- 
ditions. This racial difference is evidently inherited along with a 
number of other differences. Similarly, O. Lamarckiana, for example, 
averages much less pigment production than O. rubrinervis. 
As already mentioned, in one extreme variant of O. rubrinervis 
there was a great increase of pigment production, and the new con- 
dition is strictly inherited. The origin and hereditary behavior of 
this extreme variant or mutant, as one chooses to call it, may now 
be described. 
This particular plant!) was one of 112 offspring from four self- 
fertilized pure O. rubrinervis plants of the previous generation. A 
total of over 1000 O. rubrinervis plants of various pedigree were 
grown that season (1907). This plant was not recognized until it 
flowered, when the conspicuous dark red buds (see plate VI, fig. 8) at 
once marked it out. As already mentioned, this form was named 
O. rubricalyx. Several of its flowers were pollinated and produced 
plenty of seeds. The plant was afterward removed to the greenhouse 
and continued to bloom, the buds, however, showing a very con- 
siderable reduction in the red under greenhouse conditions, probably 
due chiefly to the reduced light. The color pattern of the buds was 
not reduced, however, to that of O. rubrinervis. This plant is a very 
1) I shall call this plant the P,, and successive generations derived from it the 
F,, Fo, etc., according to the convenient terminology for hybrids, 
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