136 LEAVES. 



destructive influence of moisture. The trees of Abys- 

 sinia are furnished with leaves of this description, for 

 they are exposed to the violence of long continued 

 rains, which nothing but this armature could enable 

 them to resist. But whether covered with varnish 

 or down, it contains minute orifices or pores through 

 which vegetables discharge the excess of their fluids, 

 and abstract nourishment from the air. 



Beneath the epidermis, we find the vessels of the 

 leaf, the tubes which ramify in every direction, and the 

 cells which occupy the intervening spaces. Two sys- 

 tems of the former are always to be found, one to dis- 

 tribute the fluids which descend through the petiole, 

 and another, to re-convey the elaborated sap to every 

 portion of the vegetable structure. 



Between these vessels, which are usually most pro- 

 minent on its inferior surface, we find the cellular sub- 

 stance of the leaf, which is not merely the seat of vege- 

 tation, but the source of those charms, which render 

 the summer's landscape more interesting and more 

 lovely, than the bleak scenery cf winter. The green 

 substance of the leaf consists entirely of these cells, 

 jvhich are filled with fluids here exposed to the action 

 of different agents, acquiring new properties and form- 

 ing the vegetable secretions. In this texture, the me- 

 dicinal and nutritive qualities of leaves reside, and they 

 supply cattle with their daily food, and insects, which 

 usually manifest a partiality for the leaves of one plant, 

 and avoid every other. Thus the Cochineal insect 

 thrives only on the Cactus, and the silk worm clings to 

 the leaf of the Mulberry, but they both die when denied 

 access to the leaves or cellular texture of their respec- 

 tive plants. These vessels constituting the cortical 

 net, consist of two layers corresponding to the two 



