EXERCISES SHOWING MINUTE STRUCTURES 



103 



In the lower epidermis will be found a considerable number 

 of small openings or stomata (singular stoma) (Figs. 77 and 

 78), leading into the irregular tunnels or intercellular spaces 

 found between the cells of the 

 mcsophyll. Each stoma or open- 

 ing is between two crescent-shaped 

 cells called guard cells. The func- 

 tion of these parts will be consid- 

 ered in Chapter X. 



Hair-like Growth on Leaves. — 

 The leaves of some plants are very 

 smooth while others have more or 

 less delicate hair-like growths 

 known as trichomes, (Fig. 79.) 

 (Chapter IV.) These trichomes 

 are so numerous on the leaves of 

 some plants as to give them the 

 appearance of velvet. These 

 structures are also found on the 

 young stems of many plants. They 

 are outgrowths of the epidermal 

 cells and present numerous very 

 interesting forms. Some of them 

 are glandular in character, and cause the plant to feel sticky to 

 the touch. They are, no doubt, protective in many ways. 



Fig. 79. — Trichomes or plant hair 

 from leaf surface. 



EXERCISES SHOWING MINUT'E STRUCTURES 



1. Pith. — Cut a vpry thin section of a pitli, mount in a drop of 

 alcohol and glycerine and examine under the microscope. Note the 

 large, tliin-walled parenchyma cells and the intercellular spaces between 

 them. Tliey resemble a large number of thin hollow balls thrown together 

 and slightly pressed out of shape where they come in contact. 



2. Examine a small piece of algae (preferably Spirogyra) iinder 

 the microscope. Note the size and form of the cells and the chromato- 

 phore. 



