132 THE ART OF CULTURE. 



the excess of food yielded by the soil at the com- 

 mencement of their development, they will require 

 for the completion of their growth, and for the for- 

 mation of their blossoms and fruits, more nourish- 

 ment 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 circum- 

 stances suffices only to complete the formation of 

 the leaves, stems, and branches. The same result 

 then ensues as when ornamental plants are trans- 

 planted 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 em- 

 ployed for the increase of their roots and leaves; 

 they spring, as it is said, into an herb or weed, 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 



o 



purpose that vines are pruned. 



A new and peculiar process of vegetation ensues 

 in all perennial plants, such as shrubs, fruit and 

 forest trees, after the complete maturity of their 

 fruit. The stem of annual plants at this period of 

 their growth becomes woody, and their leaves change 

 in color. 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 the leaves form no more wood ; 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).* Ac- 



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



