Andrew Knight (22/6. 'Treatise on the Culture of the Apple' etc. page 3.) attributed the variation of both animals and plants to a more abundant supply of nourishment, or to a more favourable climate, than that natural to the species. A more genial climate, however, is far from necessary; the kidney- bean, which is often injured by our spring frosts, and peaches, which require the protection of a wall, have varied much in England, as has the orange-tree in northern Italy, where it is barely able to exist. (22/7. Gallesio 'Teoria della Riproduzione Veg.' page 125.) Nor can we overlook the fact, though not immediately connected with our present subject, that the plants and shells of the Arctic regions are eminently variable. (22/8. See Dr. Hooker's Memoir on Arctic Plants in 'Linn. Transact.' volume 23 part 2. Mr. Woodward, and a higher authority cannot be quoted, speaks of the Arctic mollusca in his 'Rudimentary Treatise' 1856 page 355 as remarkably subject to variation.) Moreover, it does not appear that a change of climate, whether more or less genial, is one of the most potent causes of variability; for in regard to plants Alph. De Candolle, in his 'Geographie Botanique' repeatedly shows that the native country of a plant, where in most cases it has been longest cultivated, is that where it has yielded the greatest number of varieties. It is doubtful whether a change in the nature of the food is a potent cause of variability. Scarcely any domesticated animal has varied more than the pigeon or the fowl, but their food, especially that of highly-bred pigeons, is generally the same. Nor can our cattle and sheep have been subjected to any great change in this respect. But in all these cases the food probably is much less varied in kind than that which was consumed by the species in its natural state. (22/9. Bechstein in his 'Naturgeschichte der Stubenvogel' 1840 s. 238, has some good remarks on this subject. He states that his canary-birds varied in colour, though kept on uniform food.)