114 



Science of Plant Life 



for small, dotlike markings. These markings are bundle 

 scars; they show where the bundles of conductive and me- 

 chanical tissue extended outward from the stem into the 

 petiole. The shape of the leaf scar and the arrangement of 

 the bundle scars are so characteristic for many kinds of trees 

 that they may serve to identify the tree in winter. 



The bud scales also leave scars when they drop. These 

 scars are usually numerous and so closely crowded that they 

 form a roughened ring about the stem. The terminal-bud 

 scars occur at intervals, surrounding the stem or branch. The 

 lateral-bud scars occur only at the bases of the branches and 

 twigs. 



Determining annual growth of shoots from terminal-bud 

 scars. Since the terminal bud marks the end of each year's 



growth, the terminal-bud scars 

 mark off a perennial stem into 

 segments, each of which repre- 

 sents the growth of a single 

 year. Often an interesting 

 life history is suggested by the 

 varying length of the intervals 

 between the bud scars on a 

 particular stem. By a study 

 of these intervals we can de- 

 termine the seasons that were 

 favorable and those that were 

 unfavorable on account of 

 drought, excessive rain, attacks 

 of insects, or some other cause. 

 , , In the pines and spruces the 



Fig. 68. Norway spruce, showing whorls ^ ^ i j re 



of branches at end of each year's growth, year's grOWth IS marked off 



