BUDS AND BRANCHES 



103 



96. The record borne by the twig. In most cases the twig 

 bears upon its surface and in its rings of wood a fairly com- 

 plete record of the most important events of its life (fig. 90). 

 Some of the markings on the surface of a 

 twig which enable us to make out its his- 

 tory are (1) bud-scale scars (from leaf buds), 

 (2) fruit scars, (3) leaf scars. Other mark- 

 ings are found which tell less of the life 

 history of the twig than those just enumer- 

 ated, but which should also be considered, 

 namely, (4) lenticels. 



The bud-scale scars, as the name implies, 

 are the markings (figs. 86 and 88, b. *<?) left 

 by the falling of the scales when the bud 

 opened. Plants like geraniums, with naked 

 buds, do not show such scars. As the twig 

 or branch in most cases is prolonged by the 

 growth, spring after spring, of its terminal 

 bud, each ring of scars marks the beginning 

 of a new season's growth. In many trees it 

 is easy to determine the age of twigs or 

 branches by counting the number of such 

 rings (fig. 89). The distance between the 

 rings of scars depends upon the rate 01 

 lengthwise growth of the shoot; this varies 

 all the way from a fraction of an inch to 



e . 



ten feet or more per year. 



1. How many times greater was the rate 

 of growth of the central twig in figure 88 

 than the average yearly rate of figure 89 ? 



2. What was the cause of this rapid 

 growth ? (Examine a horse-chestnut tree.) 



3. If the twig in figure 89 grew unequally in different 

 years, what is a probable cause of the fact.? 



4. How did the leaves of figure 88 compare in size with 

 those of figure 89 ? Why ? 



FIG. 89. A slowly 



^' twig of hor.se- 



chestnut in winter 



condition 



,/ dormant buds; /, 

 flower-cluster scar. 



The internodes are 



numbered iu sm-ces- 

 sion (beginning at 



ig which they were 



