Tlie Emdence from Variation. 147 



justified in giving great emphasis to the law that varia- 

 bility is almost exclusively the characteristic of organ- 

 isms produced from fertilized ova. 



Darwin says ( Variation, Vol. ii. pp. 351 and 377), 

 '' AVhen we reflect on the millions of buds which many 

 trees have produced before some one bud has varied, we 

 are lost in wonder what the precise cause of each varia- 

 tion can be." *' Habit, however much prolonged, rarely 

 produces any effect on a plant propagated by buds: it 

 apparently acts only through successive seminal genera- 

 tions." 



The curious history of the naturalization of the orange 

 in Italy, quoted by Darwin on the authority of Gal- 

 lesio {Thcoria della Rijjroduzione Veg, 1816, p. 125), is 

 verv interestino^ in this connection. Durino- manv cen- 

 turies the sweet orange was propagated exclusively by 

 grafts, and so often suffered from frost that it required 

 protection. After the severe frost of 1709, and more es- 

 pecially after that of 1763, so many trees were destroyed 

 that seedlings from the sweet orange were raised, and to 

 the surprise of the inhabitants their fruit was found to 

 be sweet. The trees thus raised were larger, more pro- 

 ductive and hardier than the former kinds, and seed- 

 lings were now constantly raised. 



Hence Gallesio concludes that much more was effected 

 for the naturalization of the orange in Italy by the acci- 

 dental production of new kinds from seeds during a pe- 

 riod of about sixty years than had been effected by graft- 

 ing old varieties during many ages. 



It is hardly necessary to give other illustrations of this 

 law, fur no one with any knowledge of the subject will 

 be inclined to question it. It is strange that its signifi- 

 cance has been overlooked, but this is probably due to 

 the failure of students of the subject to perceive that it 



