dissimilarly-coloured; so that the yellow-flowered variety of either
species (and conversely with the white-flowered variety), when crossed
with pollen of its own kind, yields more seed than when crossed with
that of the white variety; and so it is when differently coloured
species are crossed. The general results may be seen in the Table at
the {106} end of his volume. In one instance he gives[228] the
following details; but I must premise that Gaertner, to avoid
exaggerating the degree of sterility in his crosses, always compares
the _maximum_ number obtained from a cross with the _average_ number
naturally given by the pure mother-plant. The white-variety of _V.
lychnitis_, naturally fertilised by its own pollen, gave from an
_average_ of twelve capsules ninety-six good seeds in each; whilst
twenty flowers fertilised with pollen from the yellow variety of this
same species, gave as the _maximum_ only eighty-nine good seed; so that
we have the proportion of 1000 to 908, according to Gaertner's usual
scale. I should have thought it possible that so small a difference in
fertility might have been accounted for by the evil effects of the
necessary castration; but Gaertner shows that the white variety of _V.
lychnitis_, when fertilised first by the white variety of _V.
blattaria_, and then by the yellow variety of this species, yielded
seed in the proportion of 622 to 438; and in both these cases
castration was performed. Now the sterility which results from the
crossing of the differently coloured varieties of the same species, is
fully as great as that which occurs in many cases when distinct species
are crossed. Unfortunately Gaertner compared the results of the first
unions alone, and not the sterility of the two sets of hybrids produced
from the white variety of _V. lychnitis_ when fertilised by the white
and yellow varieties of _V. blattaria_, for it is probable that they
would have differed in this respect.

Mr. J. Scott has given me the results of a series of experiments on
Verbascum, made by him in the Botanic Gardens of Edinburgh. He repeated
some of Gaertner's experiments on distinct species, but obtained only
fluctuating results; some confirmatory, but the greater number
contradictory; nevertheless these seem hardly sufficient to overthrow
the conclusions arrived at by Gaertn