

258 CAUSES OF VARIABILITY. Chap. XXII. 



they will be in excess ; and as growth, nutrition, and reproduc- 

 tion are intimately allied processes, this superfluity might dis- 

 turb the due and proper action of the reproductive organs, and 

 consequently affect the character of the future offspring. But 

 it may be argued that neither an excess of food nor a superfluity 

 in the organised fluids of the body necessarily induces variability. 

 The goose and the turkey have been well fed for many genera- 

 tions, yet have varied very little. Our fruit-trees and culinary 

 plants, which are so variable, have been cultivated from an 

 ancient period, and, though they probably still receive more 

 nutriment than in their natural state, yet they must have 

 received during many generations nearly the same amount ; 

 and it might be thought that they would have become habituated 

 to the excess. Nevertheless, on the whole, Knight's view, that 

 excess of food is one of the most potent causes of variability, 

 appears, as far as I can judge, probable. 



Whether or not our various cultivated plants have received 

 nutriment in excess, all have been exposed to changes of 

 various kinds. Fruit-trees are grafted on different stocks, 

 and grown in various soils. The seeds of culinary and agri- 



ing 



the last century the rotation of our crops and the manures used 

 have been greatly changed. 



Slight changes of treatment often suffice to induce varia- 

 bility. The simple fact of almost all our cultivated 

 and domesticated animals having varied in all places and 

 times, leads to this conclusion. Seeds taken from cc 

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

 manured or otherwise artificially treated, yield seedlings 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 (Crataegus oxycantha) has pro- 

 duced; yet this tree has been subjected to hardly any culti- 

 vation. In Staffordshire I carefully examined a lar^e number 



cultural plants are carried from place to place ; and dm 



rumon 



of two British plants, namely, Geranium phceum 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 flowers and foliage, to a degree which 



