The Temperature Relation 401 



industry in that section, for the wood of the peach trees 

 was entirely " unripened." 



Throughout a large portion of the zone of its culture the 

 cotton plant on well-watered and rich land grows contin- 

 uously until killed by frosts. In the same way the nas- 

 turtium and the tomato may be in full growth when killed 

 by frost. To a less extent this is true for familiar native 

 plants of the field. In spite of these facts, the impression 

 should not prevail that the vegetative period of a plant is 

 so fixed by heredity and ancestral adjustment as to be 

 incapable of responding fairly rapidly to the new environ- 

 ment. In a new region the growing season of a species or 

 variety may be changed noticeably within- a very few years. 

 Corn from the far South with a growing period of six 

 months will, if at all able to maintain itself in the North, 

 modify its period of growth so that it will mature well 

 within the season. Relatively few crops, however, are 

 able to survive and propagate themselves if left to form 

 fruit and germinate in the open, and in the relation of 

 cultivated crops to temperature the question is more 

 complex than is generally assumed. 



239. Temperature and production. As one goes north- 

 ward in the United States or in Europe, a certain general 

 change of crops is evident, indicating the universal im- 

 portance of the temperature factor in modifying produc- 

 tion. Potatoes may be grown from Mexico to Maine, but 

 throughout this whole range the growing season is well 

 within the normal length of the Maine summer. In fact, 

 in the far South two crops may be grown during a single 

 season. Corn is produced in the same region, but certain 

 strains of field corn grown in the South might not reach 

 2o 



