allowed to germinate on damp sand, were sown on the opposite sides of
pots, and the fully grown plants measured. But this plan is less
accurate, as the seeds sometimes germinated more quickly on one side
than on the other. It was however necessary to act in this manner with
some few species, as certain kinds of seeds would not germinate well
when exposed to the light; though the glasses containing them were kept
on the chimney-piece on one side of a room, and some way from the two
windows which faced the north-east. (1/7. This occurred in the plainest
manner with the seeds of Papaver vagum and Delphinium consolida, and
less plainly with those of Adonis aestivalis and Ononis minutissima.
Rarely more than one or two of the seeds of these four species
germinated on the bare sand, though left there for some weeks; but when
these same seeds were placed on earth in pots, and covered with a thin
layer of sand, they germinated immediately in large numbers.)

The soil in the pots in which the seedlings were planted, or the seeds
sown, was well mixed, so as to be uniform in composition. The plants on
the two sides were always watered at the same time and as equally as
possible; and even if this had not been done, the water would have
spread almost equally to both sides, as the pots were not large. The
crossed and self-fertilised plants were separated by a superficial
partition, which was always kept directed towards the chief source of
the light, so that the plants on both sides were equally illuminated. I
do not believe it possible that two sets of plants could have been
subjected to more closely similar conditions, than were my crossed and
self-fertilised seedlings, as grown in the above described manner.

In comparing the two sets, the eye alone was never trusted. Generally
the height of every plant on both sides was carefully measured, often
more than once, namely, whilst young, sometimes again when older, and