THE VOLATILE PAET OF PLANTS. 79 



At spring-time, in cold climates, the starch stored up 

 over winter in the new wood Qf many trees, especially the 

 maple, appears to be converted into the saccharose which 

 is found so abundantly in the sap, and this sugar, carried 

 upwards to the buds, nourishes the young leaves, and is 

 there transformed into cellulose, and into starch again. 



The sugar-beet root, when healthy, yields a juice con- 

 taining 10 to 14 per cent of saccharose, and is destitute of 

 starch. Schacht has observed that in a certain diseased 

 state of the beet, its sugar is partially converted into starch, 

 grains of this substance making their appearance. ( Wil- 

 da's Gentralhlatt, 1863, II., p. 217.) 



The analysis of the cereal grains sometimes reveals the 



presence of dextrin, at others of sugar or gum. 



Thus Stepf found no dextrin, but both gum and sugar in maize-meal, 

 {Jour, fur JPrakt. Chem., 76, p. 93;) -while Fresenius, in a more recent 

 analysis, ( Vs. St., 1, p. 180,) obtained dextrin, but neither sugar or gum. 

 The sample of maize examined by Stepf contained 3.05 p. c. gum and 

 3.71 p. c. sugar; that analyzed by Fresenius yielded 2.33 p. c. dextrin. 



Gum Tragacanth is a result of the transformation of 

 cellulose, as Mohl has shown by its microscopic study. 



5. In the animal, the substances we have been describ- 

 ing also suffer transformation when employed as food. 

 During the process of digestion, cellulose, so far as it is 

 acted upon, starch, dextrin, and probably the gums, are 

 all converted into glucose. 



c. Many of these changes may also be produced apart 

 from physiological agency, by the action of heat, acids, and 

 ferments, operating singly or jointly. 



Cellulose and starch are converted by boiling with a 

 dilute acid, into dextrin and finally into glucose. If paper 

 or cotton be placed in contact with strong chlorhydric 

 acid, (spirit of salt,) it is gradually converted into the 

 same sugar. Cellulose and starch acted upon for some 

 time by strong nitric acid, (aqua-fortis,) give compounds 

 from -which dextria may be separated. Nitrocellulose, 

 (gun cotton,) sometimes yields gum by its spontaneous 



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