140 CHEMISTRY OF PLANT LIFE 



Recent studies seem to show that in the animal body fats serve 

 an important function in connection with the production of anti- 

 bodies to disease germs. But there is as yet no evidence to show 

 that fats and oils have any similar function in plant tissues. The 

 fact that they are found almost wholly in the storage organs of 

 plants seems to indicate that their use as food reserve material is 

 their principal, if not their sole, function in the plant economy. 



B. THE WAXES 



Waxes are most commonly found in or on the skin of leaves or 

 fruits. They are similar to fats in chemical composition, except 

 that, instead of being glycerides, they are esters of monohydric 

 alcohols of high atomic weight. The term wax, when used in the 

 chemical sense, has reference to this particular type of esters 

 rather than to any special physical properties which the compound 

 possesses, and both solid and liquid waxes are known. 



Carnauba wax, found on the leaves of the wax-palm (Coper- 

 niria cerifera) contains ceryl alcohol (^aHssOH) and myricyl 

 alcohol (CaoHeiOH) esters of cerotic acid (C25H51-COOH) and 

 carnaubic acid (C23H47-COOH). It is the best known vegetable 

 wax. Poppy wax is composed chiefly of the ceryl ester of palmitic 

 acid (Ci 7 H 3 5-COOH). 



Since waxes contain no glycerol, they give no odor of acrolein 

 when heated with dehydrating agents, do not become rancid, 

 and are less easily hydrolyzed than the fats. They are soluble in 

 the same solvents as the fats, but generally to a less degree. 



The facts that waxes are impervious to water and usually 

 occur on the surfaces of plant tissues have led to the conclusion 

 that their chief function is to provide against the too-rapid loss of 

 water by evaporation from these tissues. This seems to be borne 

 out by the common experience that many fresh fruits and vege- 

 tables will keep longer without shriveling if their waxy coating is 

 undisturbed. No other function than that of regulation of water 

 losses has been suggested for the plant waxes. 



C. THE LIPOIDS 



The lipoids, or " lipins," as some authors prefer to call them, 

 are substances of a fat-like nature which are found in small quan- 

 tities in nearly all plant and animal tissues and in considerable 



