Notices of Boohs. 
533 
1877.] 
fully grown, were plainly taller and more vigorous than the self- 
fertilised ones.” Mr. Darwin, however, whom some persons 
accuse of rushing hastily to conclusions without sufficient evi- 
dence, considered it still “ quite incredible that the difference 
between the two beds of seedlings could have been due to a 
single acft of self-fertilisation.” The next year he performed an 
analogous experiment. “ I raised, for the same purpose as 
before, two large beds close together of self-fertilised and crossed 
seedlings from the carnation, Dianthus cavyopliyllus. This plant, 
like the Linaria , is almost sterile if insecfts are excluded, and 
we may draw the same inference as before, namely, that the 
parent-plants must have been inter-crossed during every — or 
almost every — previous generation. Nevertheless, the self-fer- 
tilised seedlings were plainly inferior in height and vigour to the 
crossed.” 
A formal series of experiments was then undertaken with 
various plants, and was continued for eleven years, the crossed 
plants in the great majority of cases being found to have the 
advantage. The general mode of experimentation was as 
follows : — “ A single plant, if it produced a sufficiency of flowers, 
or two or three plants were placed under a net stretched on a 
frame, and large enough to cover the plant without touching it. 
This latter point is important, for if the flowers touch the net 
they may be cross-fertilised by bees. I used at first white-cotton 
net with very fine meshes, but afterwards a kind of net with 
meshes one-tenth of an inch in diameter. On the plants thus 
protected several flowers were marked, and were fertilised with 
their own pollen ; and an equal number on the same plant, 
marked in a different manner, were at the same time crossed 
with pollen from a distincft plant. The crossed flowers were 
never castrated, in order to make the experiments as like as 
possible to what occurs in Nature with plants fertilised by the 
aid of insecfts. In some few cases of spontaneously self-fertile 
species the flowers were allowed to fertilise themseves under the 
net, and in still fewer cases uncovered plants were allowed to be 
freely crossed by the insecfts which incessantly visited them.” 
The seeds from the flowers thus treated were allowed to ripen 
thoroughly, and were then allowed to germinate, with the fol- 
lowing precautions “ The crossed and self-fertilised seeds 
were placed on damp sand, on opposite sides of a glass tumbler 
covered by a glass plate, with a partition between the two lots, 
and the glass was placed on the chimney-piece in a warm room. 
I could thus observe the germination of the seeds. Sometimes 
a few would germinate on one side before any on the other, and 
such were thrown away. But as often as a pair germinated at 
the same time they were planted on opposite sides of a pot, with 
a superficial partition between the two ; and I then proceeded 
until from half-a-dozen to a score or more seedlings, of exacftly 
the same age, were planted on the opposite sides of several pots. 
