EXERCISE 34 

 THE HISTORY OF THE GROWTH OF A BRANCH 



Materials. Twigs or short branches as used in preceding exercise. 

 This exercise is best carried out in the field, where branches may 

 be examined on the trees. 



Directions for work. Examine several branches and determine 

 the limits of last season's growth. This may be readily de- 

 termined by differences in color and general appearance of the 

 bark. The junction between the part of the twig grown last 

 season and the part a year older is marked by the bud-scale 

 scars (Exercise 33). Aided by the bud-scale scars, identify 

 each year's growth as far back along the branch as it is possi- 

 ble to distinguish these scars. What is the year of growth of 

 the oldest section of the branch the date of which you can 

 positively identify ? Is the amount of growth year by year 

 practically uniform ? If not, can you suggest possible causes 

 for difference ? 



Give attention next to the conspicuous and more or less 

 crescent-shaped scars which are distributed along the stem. They 

 are leaf scars, left when the leaves fell and indicating the 

 point of attachment of leaves. Compare with the leafy tips of 

 branches, or in winter with house plants, to secure a clear 

 notion of the relation of leaves to leaf scars. How many leaves 

 were on last season's growth-? How many the preceding season? 

 In general, is the number of leaves produced annually rather 

 uniform or does it vary widely ? The small scars within the leaf 

 scars show where fibrovascular bundles passed into the leaves. 



Reexamine the stem with reference to character and location 

 of buds. In addition to the large bud at the end of each twig 

 (terminal bud) which was studied in some of the preceding 

 exercises there are usually many buds scattered along the sides 

 of the twigs. These are called lateral buds. What is the posi- 

 tion of the lateral buds with reference to the leaf scars? What 

 was their relation to the leaves? Are they formed while the 

 leaves are yet on the branches or after the leaves have fallen ? 

 If you have watched the opening of buds in spring (Exercise 33), 



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