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 (Hlodea), or other green aquatic 
plant; bean or tropeolum, or other green leaves gathered from plants 
growing in the sunshine; a healthy potted plant; a small, fresh cutting. 
Appiiances. — 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, 
Exprertment 65. IS THERE ANY RELATION BETWEEN SUNLIGHT 
AND THE GREEN COLOR OF LEAVES ? — Place 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. 
ExpEeriMeNT 66. Do LEAVES GIVE OFF ANYTHING ELSE BESIDES 
WATER ? — Submerge a green water plant, with the cut end uppermost, in 
