Man has been able greatly to modify many vegetable productions. Witness the comparatively recent changes in the potato plant. The small, almost worthless tubers of the wild potato have changed, under the force of intelligent cultivation, to the large, starchy, nutritious vegetables, which furnish so many people a large portion of their food. Mind has been at work; mind and nature have changed the size, the quality, the productiveness of the _solatium tubcrosum;_ but neither mind nor nature, nor both combined, have, so far as we know, ever in the slightest degree changed the species. Potatoes are potatoes still, and always will be. The present law of vegetation is that intelligent cultivation of almost any plant will either change the original in one way or another, or, what is more likely, will produce several distinct varieties; but that all these changed forms are but mere modifications of the original species, and that, when deprived of intelligent cultivation, they all tend to revert to the original form. It is true that we see many and very diverse varieties of certain species, especially those that have received the most attention from the hands of man. The dog, for instance, exists as the great, shaggy Newfoundland or St. Bernard, or as the tight girted greyhound, as the petted poodle or the despised "yellow dog;" but in every case he is a dog, and not a wolf, and his fellow dogs recognize him as such, too. Hens differ amazingly; new breeds periodically come into existence and into fashion; but turn them loose, and they will all seek the barnyard, and soon your fancy breeds will become corrupt. They "revert to type." By the exercise of intelligent selection and training, man is able to emphasize certain points and to produce new breeds, but not to change the essential structure nor to alter the specific characteristics. The species are _fixed_. Huxley says: "If you breed from the male and female of the same race, you of course have offspring of the like kind, and if you make the offspring breed together, you obtain the same result, and if you breed from these again, you will still have the same kind of offspring; there is no check. But if you take members of two distinct species, however similar they may be to each other, and make them breed together, _you will find a check_. If you cross two such species with each other, then--although you may get offspring in the case of the first cross, yet, if you attempt to breed from the products of that crossing, which are what are called hybrids-- that is, if you couple a male and a female hybrid--then the result is that in ninety-nine cases out of a hundred you will get no offspring at all; there will be no result whatsoever.