130 ESSENTIALS OF BOTANY 
acid gas to escape, and by closing completely they may 
greatly check the loss of water from the plant. 
153. Chlorophyll as found in the Leaf. — Slice off a little 
of the epidermis from some such soft, pulpy leaf as that 
of the common field sorrel,! live-for-ever, or spinach ; scrape 
from the exposed portion a very little of the green pulp; 
examine with the highest power attainable with your 
microscope, and sketch several cells. Also study the 
chlorophyll in a small moss leaf, e.g., of Mnium. 
Notice that the green coloring matter is not uniformly 
distributed, but that it is collected into little particles 
called chlorophyll bodies (Figs. 98, 94). 
154. Woody Tissue in Leaves. — The veins of leaves con- 
sist of fibro-vascular bundles containing wood and vessels 
much like those of the stem of the plant. Indeed, these 
bundles in the leaf are continuous with those of the stem, 
and consist merely of portions of the latter, looking as 
if unraveled, which pass outward and upward from the 
stem into the leaf under the name of leaf-traces. These 
traverse the petiole often in a somewhat irregular fashion. 
It is now easy to see that the dots noted on the leaf-scars 
of the horse-chestnut, the Adlanthus (Fig. 49), and other 
trees, are merely the spots at which the leaf-traces passed 
from stem to petiole. 
155. Experimental Study of Functions of Leaves. — 
The most interesting and profitable way in which to find 
out what work leaves do for the plant is by experimenting 
upon them. Much that relates to the uses of leaves is 
not readily shown in ordinary class-room experiments, but 
some things can readily be demonstrated in the experi- 
ments which follow. 
1 Ruimex Acetosella. 
