110 REVIEW OF THE PRINCIPLES OF NUTRITION. 



not all to be immediately employed in building up the tissues, 

 but mostly to be stored away in reserve for future use. Such 

 deposits are made in the root of the beet, tuber of the potato, and 

 in the fruit of almost all plants. These three products, with 

 lignin, are all composed of carbon with the elements of water, — 

 gum and starch containing them in the same proportions. 



327. Sugar is sometimes produced directly from the proper 

 juice, as in the root of the beet, stalk of the maize and sugar- 

 cane ; but oftener, during germination, from the starch deposited 

 in the seed. Its composition differs from that of starch, only in 

 containing a larger proportion of the elements of water, or (what 

 is the same thing) a smaller proportion of carbon. The trans- 

 formation of starch into sugar appears to be dependent on the 

 presence of a certain substance called " diastase ; minute quan- 

 tities of which exist in seeds, and about the eyes of the potato." 



328. The similarity of these ?owx general products, in chemical 

 constitution, accounts for the facility with which they are con- 

 verted into each other in the growing plant. Thus gum is 

 converted into starch (in which state it is best adapted for pre- 

 servation), and starch is converted into sugar (131). In flowering, 

 sugar is rapidly consumed by the flower, — a portion of it being 

 reconverted into starch, and deposited in the seed. Both gum 

 and sugar appear to be converted into lignin during the growth 

 of the tissues; and this substance, in the laboratory of the chemist, 

 has been changed again into gum and sugar. 



329. Among the numerous secretions of plants which our limits 

 forbid us to consider, are the vegetable acids, containing more 

 oxygen than exists in water ; and the oils and resins, containing 

 less than exists in water, or none at all. These substances vary 

 in the different species almost to infinity, taking into their con- 

 stitution, in addition to the four organic elements, minute portions 

 of the mineral sitbstances introduced by rain-water. Their 

 peculiarities of flavor, odor, color, properties, &c. although so 

 obvious to the senses, are occasioned by differences in constitu- 

 tion often so slight as to elude the most delicate tests of the 

 chemist. 



