CUTIN 231 



protoplast, the thickness of the cuticle being proportional to 

 the amount of fat secreted by the plant. Thus heath plants, 

 which synthesize much fat, are characterized by the presence 

 of thick cuticles. The authors explain the distribution of 

 cuticle in various plants by speculations regarding the in- 

 fluence of external factors such as the relative proportion of 

 potassium and calcium, light and humidity. The presence of 

 hydroxy-acids in cuticle would appear to be established, from 

 which the authors conclude that aeration is an important 

 factor. The fact that the iodine value of the fat extracted 

 from the shoot tips of Vicia Faha was 73 as compared with 

 114 for the root apices, and that the iodine values of 90 and 

 54 were obtained for the cuticle fat of indoor forced and 

 outdoor grown rhubarb respectively, suggest that fats exposed 

 to the oxidizing and drying conditions of the open air become 

 saturated more quickly than those exposed to the atmosphere 

 of forcing sheds. Further, the authors found that the outdoor 

 rhubarb contained twice as much hydroxy-fatty acid as forced 

 rhubarb. 



With respect to the chemistry of cutin, it is concluded that 

 cutin is a complex mixture of fatty acids, both free and com- 

 bined with alcohols, that have undergone condensation and 

 oxidation ; soaps of fatty acids together with unsaponifiable 

 material which probably contains some higher alcohols, and 

 resinous substances. Cutin, unlike suberin, contains no phel- 

 lonic acid, phloionic acid (see p. 233), or glycerol. 



From these observations it will be seen that the term 

 cutin does not represent a chemical individual but an aggre- 

 gate of substances varying in specific composition but occurring 

 at the same place in the plant and having the same general 

 characters. 



Other investigations of cuticle are those of Clifford and 

 Probert * on the wax of American cotton, and of Legg and 

 Wheeler f upon the cuticle of Agave americana. The former 

 authors find the cuticle wax to contain some glycerol esters, 

 a number of monohydric alcohols, hydrocarbons, and resin 



* Clifford and Probert : " J. Text. Inst.," 1924, 15, 8, 401. 

 t Legg and Wheeler : " J. Chem. Soc," 1925, 127, 1412. 



