142 



ESSENTIALS 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- 

 section . . 

 Structure of epidermis. 

 Structure of stomata. 

 Distribution of stomata. 

 Structure and distribution of chlorophyll bodies. 



•:{ 



171. Review Summary of Functions of Leaves. 



Principal uses of 



Substances received by the leaf . 

 Substances manufactured by the leaf. 

 Substances given off by the leaf . 



flbro-vascular bundles, 

 epidermis, 

 stomata. 

 air spaces, 

 palisade-cells, 

 spongy parenchyma, 

 waxy coating, 

 hairs. 



from the air. 

 from the soil. 



into the air. 

 into the stem. 



Mineral substances accumulated in the leaf. 

 Statistics in regard to transpiration. 



1 Illustrate with sketches and diagrams. 



