42 THE VITAL FUNCTIONS. 



ficially isfFected in the laboratory of the chemist, 

 it has been found that gum and sugar are inter- 

 mediate products, or states of transition between 

 various others ; and they appear to be peculiarly 

 calculated, from their great solubility, for being 

 easily conveyed from one organ to another. 

 Starch, and lignin, on the other hand, are com 

 pounds of a more permanent character, and 

 especially adapted for being retained in the 

 organs. Starch which, though solid, still pos- 

 sesses considerable solubility, is peculiarly fitted 

 for being applied to the purposes of nourish- 

 ment: it is accordingly hoarded in magazines, 

 with a view to future employment, being to 

 vegetables, what the fat is to animals, a resource 

 for exigencies which may subsequently arise. 

 With this intention, it is carefully stored in small 

 cells, the coats of which protect it from the im- 

 mediate dissolving action of the surrounding- 

 watery sap, but allow of the penetration of this 

 fluid, and of its solution, when required by the 

 demands of the system. The tuberous root of 

 the potatoe, that invaluable gift of Providence 

 to the human race, is a remarkable example of 

 a magazine of nutritive matter of this kind. 



The lignin, on the contrary, is deposited with 

 the intention of forming a permanent part of the 

 vegetable structure, constituting the basis of the 

 woody fibre, and giving mechanical support and 

 strength to the whole fabric of the plant. These 



