DIFFERENT PARTS OF A TREE. 31 



ture, in order to keep them in a healthy, vigorous 

 state. 



When too much heat and moisture are applied to 

 a tree growing in a confined or shaded situation they 

 are imbibed by the leaf, and the consequence is that 

 the plant is elongated without its proper qualities ; 

 the leaves assume a feeble appearance, and are often 

 totally destroyed when the sun and air act on 

 them ; hence when young plants (as in seedling 

 beds in the nursery) are so confined that they can- 

 not expand their leaves so as to receive a due pro- 

 portion of sun and air, it is not to be expected 

 that they will obtain a sufficient strength and 

 vigor. 



It is proper in seedling beds to thin out the 

 young plants so soon as the leaves appear on the 

 plant, to such a distance apart, that they may have free 

 access to the sun, air, and other stimulants. This 

 fact is apparent to any careful observer who 

 will notice a quantity of seedling trees growing in 

 their natural state in woods or other places ; in this 

 situation when the young plants are grown too thick- 

 ly together, many naturally die for the want of air, 

 and the remainder in the succeeding year make a 

 healthy growth because they can then obtain a due 

 share of air and other stimulants. Now as the soil 

 at the roots of these trees is in most cases quite 

 sufficient to feed them, it is evident that suffocation 

 or want of air is the cause of the plants dying ; 

 therefore it is plain that the leaves are of great 

 importance to trees and plants. 



The leaves of trees, we are informed by botanists, 

 are analogous to the lungs of animals ; therefore 



