CONSTITUTION AND ARCHITECTURE IN THE CELL WALL 33 



acids are represented by oleic acid, C17H33COOH, and linoleic 

 acid C 17 H 31 COOH. The important fatty alcohols are cetyl C 26 , 

 myricyl C 30 , and higher homologs up to C 34 . Cerin, C30H50O2, 

 and friedelin, C 46 H 76 2 , are cyclic alcohols containing an alcoholic 

 OH and a cyclic ether bridge. In all of these aliphatic derivatives, 

 there is but one functional group per molecule. Hence, the formation 

 of waxes by esteriflcation can involve only one molecule each of 

 acid and alcohol. In addition, there are esters which yield on 

 saponification by bi-functional ohydroxy acids such as hydroxy- 

 lauric (or sabinic) and hydroxy-palmitic (or juniperic) acid. These 

 acids are joined "head to tail" to form the high molecular weight 

 polyesters known as "estolids". In general, the degree of polymeri- 

 zation in the estolids is not too high, as indicated by their melting 

 ranges and solubilities. 



The most conspicuous sources of the simpler cuticular sub- 

 stances are leaf epidermis, fruit epidermis, and seed coats. Carnauba 

 wax, from the leaf of the palm, Copernicia, contains esters of the 

 even C26-C34 alcohols with monocarboxylic acids of the same 

 chain lengths. The paraffin C 2 7H 56 also occurs. Candellilla {Eu- 

 phorbia) wax consists of 50-60 per cent n-hentriacontane (C^H^), 

 15 per cent C 30 , C 32 , C34 acids, and 5 per cent of the correspond- 

 ing alcohols. Apple cuticle contains 77-C 2 7H 56 and /?-C 2 c)H 6 o, 

 together with the C 2 6, C 28 and C 30 alcohols. 



The resistant cuticular substances are complex polymers whose 

 structural plan is still largely unknown. Three high-polymeric 

 cuticular substances have been recognized: suberin, which is 

 associated with cork or "corky" tissues; cutin, which is the common 

 cuticular ground substance present on epidermal cells in general; 

 and sporopollenin, the extremely resistant wall substance of pollen 

 grains. Sporopollenin is the most highly polymerized, most difficultly 

 saponifiable of the three, suberin is the most readily decomposed. 



Oxidative degradation of suberin yields a variety of aliphatic 

 acids, among them suberic acid, HOOC(CH 2 ) 6 COOH; phloionolic 

 acid, Ci 7 H 32 (OH) 3 COOH; phloionic acid, HOOCCi 6 H 30 (OH) 2 

 COOH; phellonic acid, C 2 iH 42 (OH)COOH; and eicosane dicarbo- 

 xylic acid; HOOC(CH 2 ) 20 COOH. The presence of hydroxyacids, 

 and dicarboxylic acids which may have been formed from hydrox- 



