RESPONSE OF THE PLANT TO ITS SURROUNDINGS 291 



dog fennel (Antheinis cotula) which formerly held undisputed 

 possession of arid places throughout the South Atlantic states. 

 A still more remarkable instance is the invasion of the Japa- 

 nese honeysuckle {Lonicera Japonica), originally introduced 

 for ornament, but which has naturalized itself within the last 

 thirty years and overrun waste places everywhere, from the 

 Gulf to the Potomac, with a vigor and luxuriance equaled 

 by few of our native species. As its beauty and fragrance 

 are even more conspicuous in a state of nature than under 

 cultivation, and as it can, moveover, be made very useful in 

 stopping gullies and washes, its phenomenally rapid occu- 

 pation of so large a territory has caused no alarm and 

 consequently attracted little attention. 



329. Climatic zones. — These are more general group- 

 ings than those we have been considering. They follow 

 in a rough way thb parallels of latitude, and are classed 

 accordingly as : (1) tropical ; (2) subtropical ; (3) temperate ; 

 (4) boreal or (on mountains) subalpine ; (5) arctic or (on 

 high mountains) alpine. Taking the cultivated plants of 

 our own country by way of illustration, we have the sub- 

 tropical zone, embracing Florida and the southern portion 

 of the Gulf states, where sugar cane, rice, and tropical 

 fruits are the staple crops. Then comes the temperate 

 zone, with three agricultural subdivisions: (a) the great 

 cotton belt, with Indian corn, sweet potatoes, and the 

 peach, melon, and fig as secondary products. Farther 

 north, in the Central and Middle Atlantic states, we find 

 (6) the region of maize, hemp, and tobacco, with grapes, 

 apples, pears, cherries, and a great variety of garden vege- 

 tables as side crops. Finally comes (c) the great wheat- 

 growing region of the North, with buckwheat, hay, and Irish 

 potatoes as subsidiary crops. 



Technically, the distribution of the natural zones of vege- 

 tation from south to north is classed under the three general 

 heads of Forest, Grass Land, and Arctic Desert, with numer- 

 ous subdivisions ill each. 



