96 PHYSIOLOGICAL PROCESSES IN PLANTS 



3. Examine a cross section of a leaf cut through some of the 

 stomata. Do they open into the air spaces ? 



4. Do you find stomata on the upper surface of the leaf ? 

 Conclusions. 1. What seems to be the use of the stomata? 



2. What might happen if they were plugged up with soot 

 or dirt? 



3. What advantage in their being on the under side of 

 the leaf? 



2. INNER STRUCTURE 



Observations. 1. Study the cross section of a leaf. Notice 

 the epidermis of the upper surface appears as a nearly color- 

 less row of cells. Are there any holes passing through 

 it? 



2. Just below the epidermis find long cylindrical cells (pali- 

 sade cells). Do they contain small granules of green matter 

 (chlorophyll) ? 



3. Under these find a spongy tissue of loosely joined cells 

 (parenchyma) with air spaces between them. Do they contain 

 as much chlorophyll as the palisade cells? 



Conclusions. 1. What is the meaning of the word "chlo- 

 rophyll"? 



2. Where do the openings of the stomata lead ? 



c. Important Functions 

 1. ABSORPTION AND RESPIRATION 



Observations. 1. Make a tube of cardboard or thick 

 paper about 1 inch in diameter and 10 inches long. Place 

 a leaf over one end, hold the tube towards the sunlight, and 

 look through it. How many leaves are necessary to absorb all 

 the light? 



2. What besides oxygen and nitrogen might pass into the 

 leaf from the air ? 



Note. Carbon dioxide is often called the "air food" of 

 plants, as distinguished from its "soil food" or water and sub- 

 stances dissolved in it. These two raw food materials meet in 



