18 PROTOPLAS:^! AND PLANT CELLS 



(C12H22O11), glucose or grape sugar (C6H12O6), fructose 

 (CeHisOe), 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), etc. 



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 maUc, 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- 



