1857.] The Leaf— Its Functions, etc. 195 



The cuticle, which covers the skeleton of the leaf and the paren- 

 chyma, is often very thin as has been said, is very porous — especially 

 on the under side. The two layers of the cuticle or epidermis seen 

 upon the superior, and inferior surfaces, armed with stomata or 

 pores are interesting in their mechanical structure, and most im- 

 portant in their offices. Having thus briefly and imperfectly sketch- 

 ed the anatomy of leaves, we pass to consider some of their offices, 

 leaving to the Botanist to describe the many and varied forms of 

 leaves which prevail, which, to name and minutely describe, would 

 fill a volume. 'T is here nature delights herself in spreading to 

 our admiring gaze an infinite and pleasing variety. Who can 

 describe the charms of Flora, who adequately image forth her 

 beauty ? Whatever earth showers from her virgin lap is mingled in 

 her shape, her color, her drapery. We attempt no description of 

 her beauty in leaf or flower. To appreciate her charms they must 

 fasten our gaze — no description will suffice. 



But we are to notice, functionally, the leaf. 



The leaves and roots are the principal organs of absorption and 

 nutrition in vegetables. The former absorb from the atmosphere 

 the substances which are subservient to growth. They are also sub- 

 servient to other purposes of the greatest importance in the economy 

 of plants. They inspire and exhale the fluids which have become 

 useless to vegetation, and it is by their agency that the sap is freed 

 of the watery juices which it contains and acquires all its nutritive 

 qualities. The leaf is the Laboratory of the tree. 'T is the faithful 

 superintending chemist that analyzes the particles which are receiv- 

 ed from the earth and air, and adjusts them in such proportions, as 

 to give to fruit and flower their fragrance, beauty, and specific 

 quality. Now the chemical compounds which afi'ord to plants their 

 principal constituents are carbon, nitrogen, hydrogen, and oxygen. 



Carbon and hydrogen invariably occur in all parts of plants. — 

 They form constituents of all their organs, and are essential to their 

 existence. The substances which constitute the principal mass of 

 every vegetable are compounds of carbon with oxygen and hydrogen, 

 in the proper relative proportions for forming water. 



Woody fiber, starch, sugar and gum, are such compounds of car- 

 bon, with the elements of water. 



Leaves probably perform in the vegetable kingdom the same 

 offices as the lungs in the animal kingdom; through them the respi- 

 ration of the plant is carried on, and at the same time a constant 



