The following case is much more remarkable, and evidently perplexed Gaertner, whose strong wish it was to draw a broad line of distinction between species and varieties. In the genus Verbascum, he made, during eighteen years, a vast number of experiments, and crossed no less than 1085 flowers and counted their seeds. Many of these experiments consisted in crossing white and yellow varieties of both _V. lychnitis_ and _V. blattaria_ with nine other species and their hybrids. That the white and yellow flowered plants of these two species are really varieties, no one has doubted; and Gaertner actually raised in the case of both species one variety from the seed of the other. Now in two of his works[227] he distinctly asserts that crosses between similarly-coloured flowers yield more seed than between 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.