20 THE PIIVSIOGNOMY AND PHYSIOLOGY 



Though cold water will not act upon starch- 

 grains, many chemical agents will, and among 

 others sulphuric acid, which not only dissolves 

 the little bladders, but has the remarkable pro- 

 perty of converting their gum into sugar. 

 Though sulphuric acid is not present in plants, 

 there is another substance which does exist in 

 them, possessing the same singular power, and 

 apparently having precisely this end to fulfil ; 

 it is called diastase, and very minute quantities 

 of it are sufficient to effect the change. Now 

 mark the wonderful arrangement by which not 

 only suitable provision is made for the support 

 and supply of the functions of vegetable life, 

 but at the same time stores are laid up for the 

 service of man. The roots of the plant draw 

 water from the soil, and perhaps some very 

 small amount of other ingredients. It is carried 

 by the vessels of the stem into the fine ramifi- 

 cations of the leaves, where it is impregnated 

 with carbonic acid, derived from the air, through 

 the pores, or stomata, which stud the under side 

 of every leaf. In the wonderful chemical labo- 

 ratory of those leaves, that carbonic acid is 

 decomposed, the oxygen given off to the air 

 again, and the carbon further elaborated into 

 starch, which is deposited as the sap circulates 

 in the cells of the cellular tissue, there to 



