IN THE SPECIES OF PRIMULA. 85 
ive agency already at work which would have carried pollen from 
one sex to the other. 
What insects habitually visit Cowslips, as is absolutely necessary 
for their regular fertility, I do not know. I have often watched 
them, but perhaps not long enough ; and only four times I have 
seen Humble-bees visiting them. One of these bees was gathering 
pollen from short-styled flowers alone, another had bitten holes 
through the corolla; and neither of these would have been effective 
in the act of fertilization: two others were sucking long-styled 
plants. I have watched Primroses more attentively during several 
years, and have never seen an insect visit them; yet from their close : 
similarity in all essential respects to Cowslips, there can hardly be 
a doubt that they require the visits of insects. Hence I am led 
to suppose that both Primroses and Cowslips are visited by moths. 
All the species which I have examined secrete plenty of nectar. 
In Primula Sinensis, when protected from insects and not arti- 
ficially fertilized, the case is somewhat, but not materially, different. 
Five short-styled plants produced up to a given period 116 flowers, 
which set only seven capsules, whereas twelve other flowers on 
the same plants artificially fertilized set ten capsules. Five long- 
styled plants produced 147 flowers, and set sixty-two capsules; so 
that this form, relatively to the other, sets a far greater number of 
capsules: yet the long-styled protected flowers do not set nearly 
so well as when artificially fertilized ; for out of forty-four flowers 
thus treated, thirty-eight set. These remarks apply only to the 
early setting of the capsules, many of which did not continue 
swelling. With respect to the product of seed, seven protected 
short-styled plants, which bore about 160 flowers, produced only 
half a grain of seed ; they ought to have produced 120 grains: so 
that the short-styled plants, when protected from insects, are nearly 
as sterile as Cowslips. Thirteen long-styled plants, which bore 
about 380 flowers, and which as we have seen set many more cap- 
sules, produced 25:9 grains of seed; they ought to have produced 
about 220 grains in weight: so that although far less fertile than 
the artificially fertilized flowers, yet the long-styled P. Sinensis, 
When protected from insects, is nearly twenty-four times as fertile 
as the short.styled when protected from insects. The cause of 
this difference is, that when the corolla of the long styled plants 
falls off, the short stamens near the bottom of the tube are neces- 
sarily dragged over the stigma and leave pollen on it, as I saw by 
hastening the fall of nearly withered flowers ; whereas in the short- 
Styled flowers, the stamens are seated at the mouth of the corolla, 
