188 TREES IN WINTER 



scars at a node as in the Horse-chestnut, or alternate with only 

 one scar at the node as in the majority of species. Alternate leaf- 

 scars may be arranged along the twig in two longitudinal rows 

 when they are said to be 2-ranhed, as in the Mulberry (fig. 103), 

 or in several rows when they are more than 2-ranked as in the 

 Poplars (fig. 100). Twigs sometimes if rapidly grown have the 

 leaf-scars which are normally opposite pulled apart to appear al- 

 ternate, but the typical condition will be found on other parts of 

 the tree. A few species like the Chestnut sometimes take the 

 2-ranked, and sometimes the more than 2-ranked position, and 

 the number of ranks in other forms may be at times somewhat 

 obscured by a twisting of the twig. The distinctions in the main, 

 however, hold good and where a doubt is likely to occur in regard 

 to the arrangement, a place has been made in the key for the 

 species in both the 2-ranked and the more than 2-ranked groups. 



The size and shape of leaf-scars are important factors in identi- 

 fication. They may be very narrow as in the Pear and their 

 upper margins may be flat or convex as in the Black Ash (p. 427) 

 or deeply notched as in the White Ash (p. 423) or form a band 

 nearly surrounding the bud as in the Sycamore (p. 349). They 

 may become dingy and inconspicuous or be sharply distinct 

 by color contrast with the rest of the twig. Thus the Elms and 

 the Poplars have their leaf-scars covered with a light-colored cork- 

 like layer which makes them conspicuous irrespective of their size. 

 Leaf-scars may be level with the twig or more or less raised with 

 tbeir surfaces parallel with the twig or making various angles 

 with it up to a right angle. Ridges in some cases run down 

 the twig from the base and corners of the leaf-scar. 



At the bases of the leaves of some species a pair of small leaflets 

 called stipules are regularly formed and leave, at the fall of the 

 leaf, more or- less definite stipule-scars at either side of the leaf- 

 scar as, shown in the Carolina Poplar (fig. 100). 



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 



