Trees of New York State 23 



Trees : 



Sargent, C. S. Manual of the Trees of Xorth America, 1905. 



Sargent, C. S. Manual of the Trees of Xorth America, 2d Ed., 1922. 

 Britton, X. L. Xorth American Trees, 1908. 



Hough, E. B. Handbook of the Trees of the Xorthern States and 

 Canada, 1907. 



"Keys", as employed in manuals, are of the dichotomous type, 

 t"hat is, two or rarely more alternatives are presented for con- 

 sideration, but one of which applies to the plant in question. 

 These alternatives are co-ordinate in rank, are equally spaced 

 from the left-hand margin, and deal with the same topic as illus- 

 trated by the simple key which follows : 



1. Leaves simple 2 



1. Leaves compound 3 



2. Leaves palmately netted- veined Maple. 



2. Leaves pinnately netted-veined Oak. 



3. Leaves palmately compound 4 



3. Leaves pinnately compound 5 



4. Leaflets three Poison Ivy. 



■L Leaflets five Virginia Creeper. 



5. Leaflets three to seven Shagbark Hickory. 



5. Leaflets seven to nine Bitter-nut Hickory. 



Given : For identification, a plant included in the key. proceed 

 as follows: Note whether the leaves are simple or compound. 

 If simple turn to the alternatives listed under 2; if compound, 

 to those listed under 3. Suppose, for the sake of illustration, 

 we assume that the leaf is palmately compound and of three leaf- 

 lets: From 1, you would proceed to 3, thence to 4. and finally to 

 the specific determination of Poison Ivy. 



It follows that the primary divisions of any key are less spe- 

 cific than the ultimate divisions. The greater the number of species 

 included, the longer is the key. Eventually, by the process of 

 elimination, the various species may be separated from each other. 



