0S THE ART OF CULTURE. 



plants from the atmosphere, in the form of carbonic acid and 

 ammonia, is limited ; they cannot assimilate more than the aif 

 contains. Now, if the quantity of their stems, leaves, and 

 branches, has been increased by the excess of food yielded by the 

 soil at the commencement of their development, they will require 

 in a given time for the completion of their growth, and for the 

 formation of their blossoms and fruits, more nourishment from 

 the air than it can afford, and consequently they will not reach 

 maturity. In many cases, the nourishment afforded by the air 

 under these circumstances suffices only to complete the forma- 

 tion of the leaves, stems, and branches. The same result then 

 ensues as when ornamental plants are transplanted from the pots 

 in which they have grown to larger ones, in which their roots 

 are permitted to increase and multiply. All their nourishment is 

 employed for the increase of their roots and leaves; they grow 

 luxuriantly, but do not blossom. When, on the contrary, we" 

 take away part of the branches, and of course their leaves with 

 them, from dwarf trees, since we thus prevent the development 

 of new branches, an excess of nutriment is artificially procured 

 for the trees, and is employed by them in the increase of the 

 blossoms and enlargement of the fruit. It is to effect this pur- 

 pose that vines are pruned. 



A new and peculiar process of vegetation ensues in all peren- 

 nial plants, such as shrubs, fruit and forest trees, after the com- 

 plete maturity of their fruit. The leaves of annual plants at 

 this period of their growth change in color ; while the leaves of 

 trees and shrubs, on the contrary, remain in activity until the 

 commencement of the winter. The formation of the layers of 

 wood progresses, the wood becomes harder and more solid, but 

 after August no more new wood is formed ; all the carbonic acid 

 which the plants now absorb is employed for the production of 

 nutritive matter for the following year : instead of woody fibre, 

 starch is formed, and is diffused through every part of the plant 

 by the autumnal sap (seve d'Aout).* According to the observa- 

 tions of M. Heyer, the starch thus deposited in the body of the 

 tree can be recognised in its known form by the aid of a good 



• Hartig, in Erdmann und Schweigger-Seidels Journal, V 217. 1835. 



