THE NUTRITIVE ORGANS OF PLANTS 55 



2. Look carefully at the scales of the terminal bud to see if they 



have any definite arrangement. State whether or not this 

 arrangement corresponds to that of the leaf scars. 



3. (Demonstration.) Examine a terminal bud from which one 



or two scales have been removed. Bud-scales are modified 

 leaves. How do these scales differ from ordinary leaves ? 

 What is the use of the scales to the bud ? How are they 

 adapted for this use ? 



C. Bud-scale scars. (These are also called annual scars because 



they are formed at the beginning of the growing season of 

 each year when the terminal bud opens and its scales fall 

 off. To prove this, remove one or two outside scales from 

 a terminal bud, and note the scar thus formed.) 

 1. How many groups of bud-scale scars or annual scars do you 



find on the twig you are studying ? 



2. Since one set is formed each spring, how many years of 

 growth are shown on the twig ? 



D. Breathing pores or lenticels. Look for small elevations on the 



bark. These locate the lenticels. Describe the lenticels. 



E. Make a careful outline drawing of the twig, showing its form, 



the position and shape of the leaf scars with their woody 

 bundles, the terminal and lateral buds, bud-scales, bud- 

 scale scars, and lenticels. Label each of the structures 

 shown in your drawing. 



67. The structure of leaves. Laboratory Study No. 35. 

 A. Parts of a leaf. 



1. Examine a simple leaf, e.g. maple, geranium, or lilac, 

 and note that it is made up of the following 

 parts : a leaf-stalk, which attaches the main part 

 of the leaf to the stem of the plant, and the 

 blade, the flat, expanded portion. 



a. How does the blade differ in form from the leaf- 



stalk? 



b. Hold the leaf to the light. How many main veins 



do you find? Where are they smallest? By 

 what are the main veins connected ? 



