110 -REVIEW OF THE PRINCIPLES OF NUTRITION: 
not all to be immediately employed in building up the tissues, 
bunt 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 “ deastase ; minute quan- 
tities of which exist in seeds, and about the eyes of the potato.” 
328. The similarity of these four 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 dgnim 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 substances 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. 
