IIJXTRR TREE STUDY 21 



The number, the size, the relation to the surface of the leaf- 

 scar, whether sunken or projecting, and the distribution of the 

 bundle-scars form important points of distinction. When they 

 are indistinct, as is frequently the case, they may be revealed if 

 a thin slice is taken off the surface of the leaf-scar. 



Buds — Buds produced at or near the nodes but not in the axil 

 of a leaf-scar are called accessory buds. Of these there are two 

 kinds: Superposed buds located above the axillary buds and 

 collateral buds located at either side of the axillary buds. The 

 former are shown in the Butternut (fig. 7) and the latter in the 

 Red Maple (fig. 8). 



Most species by the end of the growing season have formed 

 terminal buds which remain through the winter and are destined 

 to continue the growth the following spring. In some species, 

 however, such as the Mulberry (fig. 9) the terminal bud together 

 with the tip of the twig dies away and drops off before the be- 

 ginning of winter leaving a small scar at the end of the twig. 

 The presence or absence of the terminal bud is a very valuable 

 point of distinction and is used throughout in the keys. Un- 

 fortunately it is not always possible at a cursory glance to say 

 whether the terminal bud is present or absent and a hand-lens 

 must generallv be used for an accurate determination of this 

 point. In the Mulberry figured, the self-pruning scar formed by 

 the dropping off of the terminal bud is perched on the tip of 

 the twig with the topmost lateral bud obviously in the axil of 

 the last leaf-scar. Frequently, however, the self-pruning scar 

 may be nearer the lateral bud which bends in and gives the ap- 

 pearance of being terminal. The presence of a leaf-scar below it 

 shows that it is in fact axillary, but since leaf-scars are some- 

 times present toward the end of twigs without buds in their 

 axils the presence of the self-jM-uning scar at the twig end must 

 be used as the decisive sign that the terminal bud is really absent. 



Aside from the color, the presence or absence of hairs, sticki- 

 ness, fragrance and other such surface characters, the position 

 of the buds in relation to the twig may be of importance. Buds 

 that lie close up against the twig as those of the Small-toothed 

 Aspen are called oppressed, while those that project more or less 

 away from the twig as those of the Carolina Poplar (fig. G) are 

 called divergent. In the Common Locust and a few other forms 

 the buds are sunken below the surface of the twig, and can be 

 found only by cutting the twig lengthwise through the leaf-scar. 



