96 FATS AND ALLIED SUBSTANCES [ch. 



Another question to be considered is the mode of synthesis in the 

 plant of the complex fatty acids which form the components of the fats. 

 No conclusive work has been done in this direction, but many investi-; 

 gators have held the view that the fats arise from carbohydrates, notably 

 the sugars. In fact, it has been shown that in Paeonia and Ricinus, as 

 the seeds mature, carbohydrates disappear and fats are formed. 



The sequence of events, however, in the synthesis of fatty acids from 



sugars is very obscure. If we examine the formulae, respectively, of a 



hexose : 



CH2OH CHOH CHOH -CHOH -CHOH CHO 



and a fatty acid, e.g. myristic acid : 



H3C — CH2 * CH2 ' CH2 ' CH2 ' CH2 * CH2 * CH2 * CH2 ' CH2 ' CH2 ' CH2 * CH2 ' COOH 



it is seen that three main changes are concerned in the synthesis of such 

 a fatty acid from sugar, i.e. reduction of the hydroxyl groups of the sugar, 

 conversion of the aldehyde group into an acid group, and finally the 

 condensation or linking together of chains of carbon atoms. An inter- 

 esting fact in connexion with this point is that all naturally occurring 

 fatty acids have a straight, and not a branched, carbon chain and also 

 contain an even, and not an odd, number of carbon atoms. It has been 

 suggested (Smedley, etc., 15-17) that acetaldehyde and a ketonic acid, 

 pyruvic acid, may be formed from sugar. By condensation of aldehyde 

 and acid, another aldehyde is formed with two more carbon atoms. By 

 repetition of the process, with final reduction, fatty acids with straight 

 chains are produced. 



WAXES 



Waxes differ from fats in that they are esters of fatty acids with 

 alcohols of high molecular weight of the methane series in place of 

 glycerol. Such alcohols are cetyl alcohol, CigHgaOH, carnaiibyl alcohol, 

 C24H49OH, ceryl alcohol, CaeHggOH, and melissyl (or myricyl) alcohol, 

 CgoHeiOH, etc. 



Waxes occur as a deposit on the leaves, fruits and stems of many 

 plants: they constitute, for instance, the "bloom" on the Grape, the 

 Plum and the leaves of Aloe, Mesembryanthemum, etc., though they 

 rarely occur in sufficient quantity to be readily collected. Nevertheless, 

 the waxes of various plants have been isolated and analysed. The 

 following are well known since they occur in considerable amounts: 



Carnatiba wax is produced by the leaves of a Brazilian Palm (Gopernicia 

 cerifera). The leaves are detached and beaten, and the particles of wax 

 collected and melted. About 2000-4000 leaves produce 16 kilos of wax. 



