Differences in structure between the two forms.
Their degrees of fertility when legitimately and illegitimately united.
P. elatior, vulgaris, Sinensis, auricula, etc.
Summary on the fertility of the heterostyled species of Primula.
Homostyled species of Primula.
Hottonia palustris.
Androsace vitalliana.

(FIGURE 1.1. Primula veris.
Left: Long-styled form.
Right: Short-styled form.)

It has long been known to botanists that the common cowslip (Primula veris,
Brit. Flora, var. officinalis, Lin.) exists under two forms, about equally
numerous, which obviously differ from each other in the length of their pistils
and stamens. (1/1. This fact, according to Von Mohl 'Botanische Zeitung' 1863
page 326, was first observed by Persoon in the year 1794.) This difference has
hitherto been looked at as a case of mere variability, but this view, as we
shall presently see, is far from the true one. Florists who cultivate the
Polyanthus and Auricula have long been aware of the two kinds of flowers, and
they call the plants which display the globular stigma at the mouth of the
corolla, "pin-headed" or "pin-eyed," and those which display the anthers,
"thrum-eyed." (1/2. In Johnson's Dictionary, "thrum" is said to be the ends of
weavers' threads; and I suppose that some weaver who cultivated the Polyanthus
invented this name, from being struck with some degree of resemblance between
the cluster of anthers in the mouth of the corolla and the ends of his threads.)
I will designate the two forms as the long-styled and short-styled.

The pistil in the long-styled form is almost exactly twice as long as that of
the short-styled. The stigma stands in the mouth of the corolla or projects just