LEAVES 163 



Sulphuric acid is preferable for two reasons : first, because it sets 

 the gas free less rapidly than does the hydrochloric acid; and 

 second, there are not so likely to be any acid fumes which might 

 injure the plants. 



To Teachers. It is sometimes preferable to charge the water 

 before the class-room experiment. 



If the class is advanced, the charging had 'better be done during 

 the class-room experiment, but with young students the more 

 simple and direct the experiment, the better. 



Suggestion. Procure a branch of some water plant 

 such as potamogeton or other aquatic plant having stems 

 of good size. 



Tie the branch to a glass rod and place it in a tall beaker 

 or battery jar of water so that it will be entirely submerged. 



Now place the jar on the window ledge where it will 

 receive plenty of strong sunlight. 



Observe the plant. Do any bubbles collect on the leaves ? 

 If so, what are they? Look at the cut-off end of the stem. 

 What occurs there? What is it? Give reasons for your 

 answer. Of what advantage are hollow stems to water 

 plants? Do the hollow stems of land plants like bamboo, 

 rush, etc., serve the same purpose? Reasons for your 

 answer. 



146. STOMATA (optional) 



Object. To demonstrate the presence of stomata. 



Method. With a sharp knife peel off a strip of skin from 

 the under surface of any leaf and mount it in a drop of water 

 or glycerin under a cover glass. Examine it first with a low 

 power to see the cells of which the skin is made and note the 

 large number of kidney-shaped cells in pairs placed with their 

 concave sides together. These are the guard cells. Between 

 the guard cells will be seen a narrow slit, the stoma, through 



