124 THE ART OF CULTURE. 



more wood : all the carbonic acid which the plants 

 now absorb is employed for the production of nutri- 

 tive 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 observations 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 microscope. The barks of 

 several aspens and pine trees-}- 'contain so much of 

 this substance that it can be extracted from them 

 as from potatoes, by trituration with water. It 

 exists also in the roots and other parts of perennial 

 plants. A very early winter or sudden change of 

 temperature prevents the formation of this provi- 

 sion for the following year ; the wood, as in the 

 case of the vine-stock, for example, does not ripen, 

 and its growth is in the next year very limited. 



From the starch thus accumulated, sugar and 

 gum are produced in the succeeding spring, while 

 from the gum those constituents of the leaves and 

 young sprouts which contain no nitrogen are, in 

 their turn, formed. After potatoes have germi- 

 nated, the quantity of starch in them is found 

 diminished. The juice of the maple tree ceases to 

 be sweet from the loss of its sugar when its buds, 

 blossoms, and leaves attain their maturity. 



* Hartig, in Erdmann and Schweigger-S'eidels Journal, V. 217. 1835. 

 t It is well known that bread is made from the barks of pines in 

 Sweden during famines. 



