298 LAWS OF VARIATION. Chap. XXIV. 



flowers and ripen their seed within shorter and shorter periods. So 

 that the tall, slowly maturing southern varieties do not succeed in 

 New England, and the New English varieties do not succeed in 

 Canada. I have not met with any statement that the southern 

 varieties are actually injured or killed by a degree of cold which the 

 northern varieties can withstand with impunity, though this is 

 probable ; but the production of early flowering and early seeding 

 varieties deserves to be considered as one form of acclimatisation. 

 Hence it has been found possible, according to Kalm, to cultivate 

 maize further and further northwards in America. In Europe, also, 

 as we learn from the evidence given by Alph. de Candolle, the 

 culture of maize has extended since the end of the last century 

 thirty leagues north of its former boundary. 58 On the authority of 

 Linnaeus, 59 1 may quote an analogous case, namely, that in Sweden 

 tobacco raised from home-grown seed ripens its seed a month 

 sooner and is less liable to miscarry than plants raised from foreign 

 seed. 



With the Vine, differently from the maize, the line of practical 

 culture has retreated a little southward since the middle ages; 60 but 

 this seems due to commerce being now easier, so that it is better to 

 import wine from the south than to make it in northern districts. 

 Nevertheless the fact of the vine not having spread northward shows 

 that acclimatisation has made no progress during several centuries. 

 There is, however, a marked difference in the constitution of the 

 several varieties, — some being hardy, whilst others, like the muscat 

 of Alexandria, require a very high temperature to come to perfection. 

 According to Labat, 61 vines taken from France to the West Indies 

 succeed with extreme difficulty, whilst those imported from Madeira 

 or the Canary Islands thrive admirably. 



Gallesio gives a curious account of the naturalisation of the Orange 

 in Italy. During many centuries the sweet orange was propagated 

 exclusively by grafts, and so often suffered from frosts, that it re- 

 quired protection. After the severe frost of 1709, and more especially 

 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 productive, and hardier than the old kinds ; and seedlings are 

 now continually raised. Hence Gallesio concludes that much more 

 was effected for the naturalisation of the orange in Italy by the 

 accidental production of new kinds during a period of about sixty 

 years, than had been effected by grafting old varieties during many 

 ages. 62 I may add that Risso e3 describes some Portuguese varieties 



58 ' Geograph. Bot.,' p. 337. p. 339. 



59 'Swedish Acts,' Eng. translat., 6l ' Gard. Chronicle,' 1862, p. 235. 

 1739-40, vol. i. Kalm, in his 'Travels,' C2 Gallesio, ' Teoria della Ripro- 

 vo\. ii. p. 166, gives an analogous duzione Veg.,' 1816, p. 125 ; and 

 case with cotton-plants raised in New ' Traite du Citrus,' 1811, p. 359. 

 Jersev from Carolina seed. U3 ' Essai sur l'Hist. des Orangers,' 



60 De Candolk, 'Geograph. Bot..* 1813, p. 20, &c. 



