10 ILLINOIS NATURAL HISTORY SURVEY MANUAL 3 



down in outline form and generally are arranged in pairs, so 

 that a choice can be made between important characters first, 

 less important characters second and still less important char- 

 acters third. By continued choosing as the outline proceeds, a 

 point is reached where no further choice is possible, and the 

 final distinguishing characteristic tells exactly the name of the 

 shrub. 



As a further example, let us "run down" in the key to genera, 

 page 17, two wild shrubs with which we already are familiar. 

 One of them, let us say, is a wild juniper, the other a dogwood. 

 The key begins with two contrasting lines labeled I and II, 

 the first of which says "Leaves very narrow; linear, or scalelike, 

 and small," the second, "Leaves broader, with proper blades; 

 not pinelike." Obviously line I describes the leaves of the juni- 

 per and line II the leaves of the dogwood. Hence we must 

 search for the name of our juniper under I and the name of 

 our dogwood under 11. Taking the juniper first, since it comes 

 in the first part of the key, we find set in under I two lines 

 labeled A. The first says, "Leaves evergreen, glabrous ; more 

 than ]/i inch long." The second says, "Leaves persistent but not 

 evergreen, pubescent; less than i^ inch long." The leaves on 

 our juniper fit the description given by the first A, and under it 

 we find two lines labeled with uncapitalized a's, in which the 

 descriptions contrasted are "Leaves apparently in 2 ranks; 

 green above," and "Leaves in whorls of 3 ; with a white line 

 above." Examining our juniper carefully, we find that the 

 leaves are set three in a ring around the stem and that each 

 leaf does have a fine white line on the upper side, which is ex- 

 actly what the key requires. So we know that the juniper is to 

 be looked for under the botanical genus Juniperus, on page 27 

 in the body of this manual. 



Now, let us see what we can do about the dogwood. Since we 

 know it is included under II in the key, we start there. We find 

 first a line labeled A, which reads, "Leaves simple, though often 

 toothed or lobed," and further down in the key we find, on 

 page 21, another line labeled A, which reads "Leaves definitely 

 compound, composed of 2 or more leaflets." Our dogwood's 

 leaves are simple, that is, each one is a single piece and is not 

 made up of two or more small, leaflike pieces. Hence, we know 

 we will find it somewhere in the part of the outline included 

 under the first A, on page 17. The following line, labeled B, 



