44 The New York State College of Forestry 



in the bud, capped by a growing point which continues to form 

 new nodes for a time, or during the remainder of the summer. 

 By far the majority of the trees of the North Temperate Zone 

 exhibit definite growth, which ceases by July or August after 

 which no new growth in length takes place. In other instances 

 the growth of the season may branch or longitudinal growth is 

 indefinite and continues into tlie autumn until stopped by cold 

 weather. In the latter case, the last formed parts, being soft and 

 tender, are then usually winter-killed, resulting in a dead stub as 

 in the case of the Staghorn Sumach. 



New leaves are borne laterally at the nodes on the new growth, 

 one or more as the case may be, and as early as June, the buds 

 for the following season begin to form in their axils. By mid- 

 summer, on trees with definite growth, elongation of the new 

 shoots has ceased, the buds have usually attained their full winter 

 size, and the remainder of the season is devoted to the ageing 

 of the new tisues, preparatory to withstanding the rigors of 

 winter. 



Leaf Fall 



As autumn approaches, trees with deciduous leaves make ready 

 for leaf-fall while in persistent leaves, metabolism ceases or is 

 greatly inhibited and certain changes occur preparatory to the 

 winter season. Prior to leaf -fall, an absciss or fission layer of loose 

 cells forms across the base of the petiole at its place of insertion 

 on the twig. This includes all the tissues at that point aside from 

 the vascular bundles leading from the stem into the petiole (leaf- 

 traees). Subsequently a corky layer (periderm) forms under the 

 absciss layer and nature's preparations for leaf -fall are complete. 

 With the advent of the autumn rains or the formation on frosty 

 nights of ice crystals between the cells of the absciss layer which 

 exert a prying action, the leaf eventually snaps ofi^' at the base of 

 the petiole, leaving a leaf-scar protected by a coating of periderm. 



Winter Habit 



The winter habit, especially of those species in which the foliage 

 is deciduous, is of diagnostic value in identification and many 

 species can be distinguished at some distance by the experienced 

 observer by this character alone. Two general types of branch- 

 ing of the trunk are recognized which, however, undergo many 

 minor variations, the excurrent or upright, and the deliquescent 

 or spreading. In the former, the primary axis or bole is con- 



