18 PROTOPLASM AND PLANT CELLS 
(Cy2H22011), glucose or grape sugar (C»Hi20¢), fructose 
(CeHi20¢), etc. 
29. Cane sugar is found in great quantities in the cell 
sap of the sugar cane, sugar beet, sugar maple, sorghum, 
Indian corn and many other plants. The first two plants 
produce the bulk of the sugar of commerce. In many 
fruits, such as grapes, cherries, gooseberries, figs, etc., 
glucose is present, while in still others, e.g. pineapple, 
peach, plum, strawberries, etc., the two are mixed. 
Fructose, as the name implies, is found in many fruits, 
e.g. the grape. In many, if not in most plants glucose 
seems to be the form in which green cells manufacture 
their food, storing up the excess over immediate consump- 
tion usually as starch, from which it is again obtained as 
glucose. Inulin is found mostly in plants of the sunflower 
family, e.g. sunflower (Helianthus), Dahlia, elecampane 
(Inula), ete. 
30. The organic acids found in the cell sap may occur 
in acid form, but frequently are found as acid salts of 
calcium or potassium or some other base. The most 
common of these acids are malic, citric, tartaric and ox- 
alic. ‘They seem to be present in some cases as food for 
the plant while in others they doubtless help to keep the 
cell turgid by raising the osmotic pressure within the cell 
to the proper degree. 
31. Among the substances found in the cell sap in so- 
lution are certain compounds known as alkaloids. These 
are perhaps in some cases products of the breaking down 
of more complex substances and to be looked on as a sort 
of excretion product comparable to urea in animals. 
However, in certain plants they may serve as reserve 
food as they are used up by the plant if no other food is 
available. They are nitrogenous compounds of compli- 
