38 



disappearance. On a few species like the Birches, Cherries, and 

 Honey Locust they persist for many years. 



The distribution of lenticels has not yet been systematized. They 

 are distributed rather uniformly over the newer growth but are ir- 

 regularly spaced. In some species they seem to be somewhat clus- 

 tered just below the nodes and in others like Honey Locust they are 

 more numerous on the lower side of horizontal branches. 



The pith usually occupies the central portion of twigs, branchlets, 

 and roots. It is composed of thin-walled cells which are loosely ag- 

 gregated. It seldom increases in size after the first year. The pith 

 of a tree 100 years old is usually not wider than that in a year old 

 twig of the same species. It becomes functionless early in the life 

 of a tree. 



The pith of conifers is rather uniform in outline, structure, and 

 color, but in the broad-leaved species it is very variable. In most 

 species it is small in proportion to the size of the twigs, but in a 

 tew species like Sumach, Elder, Sassafras, Ailanthus, and Kentucky 

 Coffee-tree it is relatively large. The outline in cross section may 

 be 5-angled or star-shaped as in the Oaks, Chestnut, and Aspens, 

 3-angled as in Alder and some Birches, angular as in Common Locust, 

 circular as in Elm, and ovoid as in Basswood. As a rule the pith 

 is continuous, but in a few species like Black Walnut, Butternut, 

 and Hackberry it is chambered. A few species like Catalpa have 

 continuous pith except at the nodes where it is sometimes chambered. 

 A less distinct separation of the pith is found in Black Gum, Papaw, 

 Tulip Tree, and the Magnolias where plates of .stone cells occur. The 

 color of the pith may be white as in the Sugar Maple, pinkish as in 

 Red Maple, brown as in Striped Maple, Mountain Maple, Sumachs, 

 and Walnuts, red as in Kentucky Coflfee-tree, or greenish as in Shad 

 Bush. 



4. Buds: 



In temperate and colder climates the growing season extends over 

 a part of the year only. During the warmer part of the year vegeta- 

 tion is active, but as soon as the weather becomes cooler, many an- 

 nual plants die while others make special preparation for the win- 

 ter. One of the preparations is the formation of buds. They are 

 formed in most trees and shrubs of cold and arid climates. If we 

 examine a twig from one of our common trees in the month of July 

 we can usually find buds starting to develop in the axils of the 

 leaves. They continue to develop until they have reached a certain 

 size, and then remain in an inactive condition for a few months in 

 winter, only to become active again when favorable growth condi- 

 tions return in spring. A year usually includes a period of rest 

 alternating with a period of activity. Buds may be divided into 



