382 PHYSICAL GEOGRAPHY. 



to observe the contrast in the aspect of the vegetation of its northern 

 and southern portions, caused by the different temperature consequent 

 upon the difference in altitude. The flora of New England has been 

 classed in two divisions, based upon this fact, which may be termed the 

 Alleghanian and the Canadian, because they seem to correspond with 

 the faunas of the same names described in the previous chapter. Of 

 course, however, no separating line, or definite and sudden change, is 

 anywhere noticed. The transition is gradual, some species becoming 

 scarce and finally disappearing, while others first appear in small num- 

 bers, but increase as the traveller advances, and at length supply the 

 place of the former as the prevailing forms of vegetation. Many other 

 species, probably one half in number of our whole flora (not being so 

 readily influenced by a difference of temperature), have a range extending 

 over the entire state. If it were attempted to draw the line between 

 these divisions, on each side of which would of course be included 

 species more particularly characteristic of the other, it might be extended, 

 approximately, from North Conway to Lake Winnipiseogee, and thence 

 to Hanover or vicinity. The transition area is thus at an elevation of 

 about five or six hundred feet above the sea, corresponding approxi- 

 mately to the isothermal line of 45 mean annual temperature, or to 20 

 during the winter and 65 during the summer months. 



Among the species which are characteristic of the Alleghanian divi- 

 sion, but find their northern limit before reaching this line or soon after 

 it is crossed, may be mentioned the chestnut, the white oak, spoonwood 

 or mountain laurel, and the frost grape ( Vitis cordifolia). The range of 

 our pines and walnuts, of white or river maple, red oak, and hemlock, is 

 also mainly southern. 



The most characteristic trees of the Canadian division are sugar maple, 

 beech, balsam fir, black and white spruce, and arbor-vitas; among its 

 shrubs are the mountain and striped maples, and the mountain ash. Of 

 these the white spruce and arbor-vitae have the most limited range ; the 

 former is abundant about Connecticut lake, but occurs rarely, if at all, 

 south of Colebrook; the latter, often incorrectly called "white cedar," 

 is also common in this section, extending south to the vicinity of the 

 White Mountains. It is also occasionally found in highland swamps 

 farther south. 



