opponent. Therefore, of the seventy-three crossed plants, sixty-eight
grew to a greater height than the self-fertilised plants, to which they
were opposed.

In the right-hand column of figures, the difference in height between
the crossed and self-fertilised plants in the successive generations is
seen to fluctuate much, as might indeed have been expected from the
small number of plants measured in each generation being insufficient to
give a fair average. It should be remembered that the absolute height of
the plants goes for nothing, as each pair was measured as soon as one of
them had twined up to the summit of its rod. The great difference in the
tenth generation, namely, 100 to 54, no doubt was partly accidental,
though, when these plants were weighed, the difference was even greater,
namely, 100 to 44. The smallest amount of difference occurred in the
fourth and the eighth generations, and this was apparently due to both
the crossed and self-fertilised plants having become unhealthy, which
prevented the former attaining their usual degree of superiority. This
was an unfortunate circumstance, but my experiments were not thus
vitiated, as both lots of plants were exposed to the same conditions,
whether favourable or unfavourable.

There is reason to believe that the flowers of this Ipomoea, when
growing out of doors, are habitually crossed by insects, so that the
first seedlings which I raised from purchased seeds were probably the
offspring of a cross. I infer that this is the case, firstly from
humble-bees often visiting the flowers, and from the quantity of pollen
left by them on the stigmas of such flowers; and, secondly, from the
plants raised from the same lot of seed varying greatly in the colour of
their flowers, for as we shall hereafter see, this indicates much
intercrossing. (2/3. Verlot says 'Sur la Production des Variétés' 1865