22 The Garden. 



leaves are extensions of the green layer of the bark (which, 

 where no proper leaves exist, fulfills their function) expanded 

 into thin lamina and strengthened by woody fibers connected 

 with the liber^ or inner bark, and with the wood. These woody 

 fibers form their frame- work, and afford, at the same time, by 

 their microscopic ramifications, a complete and beautiful system 

 of veins. The leaf, therefore, like the stem, consists of two 

 distinct parts, the cellular and the woody. The cellular por- 

 tion is not the structureless, pulpy mass which it appears to be 

 to the naked eye, but presents a regular and beautiful arrange- 

 ment of cells. The woody part forming the veins, and having, 

 as we have seen, a double origin, is arranged in two layers ; the 

 upper, arising from the wood, and conveying the ascending 

 sap to every part of the leaf, and the lower, connected with 

 the liber^ and establishing a communication with the bark, by 

 means of which the assimilated juices pass downward. En- 

 casing the whole of this wonderfully beautiful apparatus is the 

 epidermis^ or skin, pierced by numerous invisible pores or holes, 

 called stomates, through which the plant breathes and per- 

 spires. 



It would be interesting, in connection with the foregoing 

 brief outline of the structure of the leaf, to give some account 

 of the different forms of leaves, their various modifications, 

 and their systematic and beautiful arrangement on the stem ; 

 but as the practical ends we have in view do not require us to 

 pursue the subject further in this direction, we must forego it. 



Leaves have been called the lungs of plants. They are 

 something more than this, being not only organs of respiration, 

 but of perspiration and digestion also. They are, at the same 

 time, stomach, lungs, and skin. They receive the crude sap 

 from the roots through the stem, and, by means of exposure to 

 air and light, the decomposition of water and carbonic acid, 

 and the throwing off of superfluous moisture, condense it and 

 change it into organizable matter — the true food of plants. 

 This elaborated sap is sent immediately downward, to serve for 

 the nourishment of every part. 



