KEVIEW ON STRUCTURE OF LEAVES 



273 



types of epidermal hairs. What use could be suggested for the 

 dense coat of hairs on leaves of shepherdia? Fig. 412. 



Note. — To study leaf tissues : A number of leaves can be com- 

 pared by making free-hand cross-sections of leaves held between 

 two pieces of pith or cork, and mounting tiie material in water. 

 Study such leaves as ivy (Hedera 

 helix), begonia, cyeas, geranium, 

 and corn. Note the number of 

 layers of palisade cells, the spongy 

 parenchyma, the epidermal lay- 

 ers. Which cells bear chlorophyll? 

 Write a brief description of the 

 tissues of each leaf and make a 

 drawing of the geranium. 



To study stomates in cross - 

 section : In the cross-sections of 

 leaves of geranium, corn, ivy, lih^, 

 or spider-lily prepared for the above experiment, look for the stomates 

 and make a careful drawing from the one you can see best. 



Study of stomates in surface vieto : From the under surface of 

 leaves of geranium and impatiens peel bits of epidermis by tearing 

 the leaf. Mount these in water and examine under low power. Are 

 the stomates scattered or in grcups? With aid of a higher power 

 draw a few stomates showing their guard cells and the surrounding 

 epidermal cells. Make a similar study and sketch of the epidermis 

 torn from the under surface of a Begonia sangulnea leaf. 



Breathing-pores are known as siomata, singular stoma; also as 

 stomates, singular stomate. 



417. Leaf-scar of the plane tree or 

 sycamore. The scar surrounds 

 the bud, which was covered by 

 the hollow base of the petiole. 



Looking for light. 



