142 ELEMENTS OF BOTANY 
the petiole in such a way that the latter finally breaks off 
across the surface of the layer. A waterproof scar is thus 
already formed before the removal of the leaf, and there 
is no waste of sap dripping from the wound where the 
leaf-stalk has been removed, and no chance for molds to 
attack the bark or wood and cause it to decay. 
169. Tabular Review of Experiments. — [Continue the table from 
Sect. 102.) 
170. Review Summary of Minute Structure of Leaves. 
Layers of tissue seen on a cross- ig 
section are ie 
Structure of epidermis. 
Structure of stomata. 
Distribution of stomata. 
Structure and distribution of chlorophyll bodies. 
171. Review Sunimary of Functions of Leaves. 
fibro-vascular bundles. 
epidermis. 
stomata. 
air spaces. 
palisade-cells. 
spongy parenchyma. 
Principal sUsessOh. cy ok Go a ee ie ae wa 
waxy coating. 
hairs. 
. ( from the air. 
Substances received by the leaf Saar : 
c l from the soil. 
Substances manufactured by the leaf. 
f into the air. 
Substances given off by the leaf es 
Z L into the stem. 
Mineral substances accumulated in the leaf. 
Statistics in regard to transpiration. 
' Tlustrate with sketches and diagrams. 
