Origin of Species Variorum

gained, in the case of dimorphic and trimorphic plants, at the expense of all the plants of the same form being rendered more or less sterile when united, and producing more or less sterile offspring. With respect to the steps by which it is probable that plants have been rendered dimorphic and trimorphic, want of space prevents my entering on the subject; but I will add that there is no special difficulty in this having been effected through variability, through the good gained by the prepotency of one sort of pollen over another, and through the accumulative action of natural selection.

Fertility of Varieties when Crossed, and of their Mongrel Offspring .

It may be urged, as a most forcible argument, that there must be some essential distinction between species and varieties, and that there must be some error in all the foregoing remarks, inasmuch as varieties, however much they may differ from each other in external appearance, cross with perfect facility, and yield perfectly fertile offspring. With some exceptions, presently to be given, I fully admit that this is the rule. ↑ But the subject is surrounded by difficulties, for, looking to varieties produced under nature, ... if two forms hitherto reputed to be varieties be found in any degree sterile together, they are at once ranked by most naturalists as species. For instance, the blue and red pimpernel, ... which are considered by most botanists as varieties, are said by Gärtner not to be quite fertile when crossed, and he consequently ranks them as undoubted species. If we thus argue in a circle, the fertility of all varieties produced under nature will assuredly have to be granted.

If we turn to varieties, produced, or supposed to have been produced, under domestication, we are still in- volved