8 USING THE KEYS. 



that there are three species with only 3 leaflets to each of the 

 compound leaves ; although the characteristic white fruit may 

 not be in evidence, my observation that it is a climber, leading 

 through the sequence I to 2; 2 to 3, satisfies me that I have 

 seen the poison ivy, Rhus radicans, in one of its protean forms. 

 Later I may chance to find it in the grass. In this guise, I 

 should trace it through Key C (p. 34) as an underbrush, coming 

 to the same result by the steps I to 15; 15 to 38; 38 to 39; 

 39 to 54; 54 to 55. In its bushy southern form, and with more 

 lobed leaves, I should trace the scarcely separable poison oak, 

 R. T^oxicodcndron, through Key B (p. 19) by the steps i to 33 ; 

 33 to 61 ; 61 to 62; 62 to 149; 149 to 150; 150 to 151, where I 

 get a cautionary signal; 151 to 152. In addition to learning 

 this dangerous plant, I may have satisfied myself incidentally 

 that the harmless Virginia creeper can be distinguished from 

 it by having 5 leaflets in each leaf, and by climbing by tendrils 

 opposite the leaves. 



An entomologist comes to me with a branch of a tree badly 

 infested with scale insects. He thinks that he knows the tree, 

 but wishes to be sure of it because the owner and his neighbors 

 can not say what it is. The Synopsis of Groups leads me to 

 Key A (p. n). It is obviously deciduous, not at all prickly or 

 spiny, with rounded twigs, opposite leaves that are rather large 

 and pinnately compound with five or seven somewhat toothed 

 short-stalked leaflets, green on both sides. Through Key -A, I 

 go by the successive steps i to 26; 26 to 39; 39 to 104; 104 to 

 112. Here I cut the twig cleanly across midway between two 

 nodes and find that the pith is of moderate diameter as com- 

 pared with elder-pith; and the succeeding steps are 112 to 113, 

 and 113 to 114, where I find that the scars from which last 

 year's leaves have fallen are squared off below this year's twigs 

 or any undeveloped buds of last season, so that I am convinced 

 that it is a Fraxinus. In the key to the species of ash (p. 158) 

 I go successively from i to 2'; 2 to 3 ; 3 to n; n to 12; 12 to 

 14, where I find it to be Fraxinus lanceolata. Reference to the 

 Cyclopedia gives fuller information about the tree. 



