168 PRACTICAL COURSE IN BOTANY 



Sketch the section of your specimen as it appears under 

 the microscope. It will perhaps differ in some details from 

 the one shown in the figure, but you can recognize and label 

 the corresponding parts. Be sure that your drawing repre- 

 sents accurately the relative size and shapes of the different 

 kinds of cells. 



It is in the upper surface, where the chlorophyll particles 

 abound, that the manufacture of food goes on most actively, 

 and from the under surface, where the stomata are situated, 

 that transpiration takes place and air and other gases pass 

 to and from the interior. These facts have important bear- 

 ings on the growth and external characters of leaves. 



Practical Questions 



1. Explain why a plant cannot thrive if its stomata are clogged with 

 foreign matter. (179; Exp. 64; 184.) 



2. Mention some of the ways in which this might happen. (181.) 



3. Why must the leaves of house plants be washed occasionally to keep 

 them healthy? (179,181.) 



4. Why is it so hard for trees and hedges to remain healthy in a large 

 manufacturing town ? 



V. FOOD MAKING 



Material. — A sprig of pondweed, mare's-tail {Hippuris), hornwort 

 (Ceratophyllum), marsh St.-John's-wort (Elodea), or other green aquatic 

 plant ; bean or tropseolum, or other green leaves gathered from plants 

 growing in the sunshine ; a healthy potted plant ; a small, fresh cutting. 

 Appliances. — A shallow dish of water and two glass tumblers or wide- 

 mouthed jars ; a bent glass or rubber tube ; a piece of black cloth or paper ; 

 a half pint of alcohol ; iodine solution ; a glass funnel or a long-necked 

 bottle from which the bottom has been removed. 



Experiment 65. Is there any relation between sunlight 

 AND THE green COLOR OF LEAVES ? — Placc a seedling of oats, or other 

 rapidly growing shoot, in the dark for a few days, and note its loss of 

 color. Leave it in the dark indefinitely, and it will lose all color and die. 

 Hence we may conclude that there is some intimate connection between 

 the action of light and the green coloring matter of leaves. 



Experiment 66. Do leaves give off anything else besides 

 WATER ? — Submerge a green water plant, with the cut end uppermost, in 



