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-f or-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 3Inium. 



Notice that the green coloring matter is not uniformly 

 distributed, but that it is collected into little particles 

 called chlorophyll bodies (Figs. 93, 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 Ailanthus (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 liumex Acetosella, 



