PLANT PHYSIOLOGY AS RELATED TO PRUNING 29 



33. Leaf formation takes place immediately in rear of 

 the stem apex. In some plants (apple) the leaves occur 

 in spiral order, in others opposite (lilac), in still others 

 alternately (elm) and so on. Incipiently, they are tiny 

 swellings, but soon they flatten and grow more rapidly 

 than does the stem apex, over which they curve more or 

 less to form a bud. In few trees does this leafy axis con- 

 tinue to extend during the growing season. Where ex- 

 tension occurs each leaf is left behind in the spiral, the 

 whorl or other natural formation as the tip moves 

 forward. New points of growth are usually differentiated 

 later as buds in the axils of the leaves ; and when the 

 leaves fall at the end of the growing season these buds 

 become 



34. Resting buds. In most trees and shrubs, at least 

 in temperate and cold climates, the shoot axis terminates 

 in late summer or early fall in a bud which is said to re- 

 main dormant until the following spring, so also do the 

 axillary buds. This dormancy is not total, since there is 

 some slight growth activity, except perhaps during the 

 coldest weather (54, 55). The resting buds are very 

 short leaf axes covered by bud scales (specialized leaves) 

 which serve as protectors of the more important internal 

 parts. While the buds are said in the fall and the winter 

 to be resting or dormant, they may have been ready for 

 the "rest" as early as July. They do not, however, usually 

 appear to be resting until the leaves fall. In spring with the 

 return to conditions favorable to growth activity the rest- 

 ing buds vapidly unfold, either a leafy shoot (quince, dier- 

 villa) a flower (peach, golden bell Forsythia, Fig. 296), a 

 cluster of flowers (cherry, spice bush Lindcra) or a 

 cluster containing both leaves and flowers (apple, thorn 

 Crat&gus) . 



35. The types of stem extension from resting buds, 



though diverse, may be grouped in two classes, though 

 these may present numerous cases of over-lapping. 



