has made some observations on the absolute sterility of a purple and white
primrose (Primula vulgaris) when fertilised by pollen from the common primrose
('Journal of Proc. of Linn. Soc.' volume 8 1864 page 98); but these
observations require confirmation. I raised a number of purple-flowered long-
styled seedlings from seed kindly sent me by Mr. Scott, and, though they were
all in some degree sterile, they were much more fertile with pollen taken from
the common primrose than with their own pollen. Mr. Scott has likewise
described a red equal-styled cowslip (P. veris ibid page 106), which was found
by him to be highly sterile when crossed with the common cowslip; but this was
not the case with several equal-styled red seedlings raised by me from his
plant. This variety of the cowslip presents the remarkable peculiarity of
combining male organs in every respect like those of the short-styled form,
with female organs resembling in function and partly in structure those of the
long-styled form; so that we have the singular anomaly of the two forms
combined in the same flower. Hence it is not surprising that these flowers
should be spontaneously self-fertile in a high degree.)

These facts with respect to plants show that in some few cases certain
varieties have had their sexual powers so far modified, that they cross
together less readily and yield less seed than other varieties of the same
species. We shall presently see that the sexual functions of most animals and
plants are eminently liable to be affected by the conditions of life to which
they are exposed; and hereafter we shall briefly discuss the conjoint bearing
of this fact, and others, on the difference in fertility between crossed
varieties and crossed species.

DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY WHICH IS GENERAL WITH
SPECIES WHEN CROSSED.

This hypothesis was first propounded by Pallas (16/28. 'Act. Acad. St.