With respect to
the rarity of P. veris in western Scotland, see H.C. Watson 'Cybele Britannica'
2 page 293.)
The cowslip and primrose, when intercrossed, behave like distinct species, for
they are far from being mutually fertile. Gartner crossed 27 flowers of P.
vulgaris with pollen of P. veris, and obtained 16 capsules; but these did not
contain any good seed. (2/5. 'Bastarderzeugung' 1849 page 721.) He also crossed
21 flowers of P. veris with pollen of P. vulgaris; and now he got only five
capsules, containing seed in a still less perfect condition. Gartner knew
nothing about heterostylism; and his complete failure may perhaps be accounted
for by his having crossed together the same forms of the cowslip and primrose;
for such crosses would have been of an illegitimate as well as of a hybrid
nature, and this would have increased their sterility. My trials were rather
more fortunate. Twenty-one flowers, consisting of both forms of the cowslip and
primrose, were intercrossed legitimately, and yielded seven capsules (i.e. 33
per cent), containing on an average 42 seeds; some of these seeds, however, were
so poor that they probably would not have germinated. Twenty-one flowers on the
same cowslip and primrose plants were also intercrossed illegitimately, and they
likewise yielded seven capsules (or 33 per cent), but these contained on an
average only 13 good and bad seeds.
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