246 CAUSES OF VARIABILITY. Chap. XXIL 



"bility. The simple fact of almost all our cultivated plants 

 and domesticated animals having varied in all places and at 

 all times, leads to this conclusion. Seeds taken from common 

 English forest-trees, grown under their native climate, not 

 highly manured or otherwise artificially treated, yield seed- 

 lings which vary much, as may be seen in every extensive 

 seed-bed. I have shown in a former chapter what a number 

 of well-marked and singular varieties the thorn (Cratcegus 

 oxycaniha) has produced : yet this tree has been subjected to 

 hardly any cultivation. In Staffordshire I carefully examined 

 a large number of two British plants, namely Geranium pliceum 

 and pyrenaicum, which have never been highly cultivated. 

 These plants had spread spontaneously by seed from a 

 common garden into an open plantation ; and the seedlings 

 varied in almost every single character, both in their flower 

 and foliage, to a degree which I have never seen exceeded ; 

 yet they could not have been exposed to any great change in 

 their conditions. 



With respect to animals, Azara has remarked with much 

 surprise, 12 that, whilst the feral horses on the Pampas are 

 always of one of three colours, and the cattle always of a 

 uniform colour, yet these animals, when bred on the un- 

 enclosed estancias, though kept in a state which can hardly 

 be called domesticated, and apparently exposed to almost 

 identically the same conditions as when they are feral, never- 

 theless display a great diversity of colour. So again in India 

 several species of fresh- water fish are only so far treated 

 artificially, that they are reared in great tanks; but this 

 small change is sufficient to induce much variability. 13 



Some facts on the effects of grafting, in regard to the 

 variability of trees, deserve attention. Cabanis asserts that 

 when certain pears are grafted on the quince, their seeds yield 

 a greater number of varieties than do the seeds of the same 

 variety of pear when grafted on the wild pear. 14 But as the 

 pear and quince are distinct species, though so closely related 



» 'Quadruples da Paraguay,' 1839, pp. 266, 268, 313. 

 1801, torn. ii. p. 319. u Quoted by Sageret, ' Pom. Phys., 



13 McClelland on Indian Cyprinidae, 1830, p. 43. This statement, how- 



'Asiatic Researches,' vol. xix. part ii., ever, is not believed by Decaisne, 



