500 FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES III 



amorphous lignin is intercalated between cellulose rodlets or lamellae. 

 In both cases the cellulose is masked by the incrustation. For example, 

 it is only with difficulty that the cellulose can be dissolved out of wood 

 with Schweizer's reagent, and hitherto could not be eliminated at 

 all in this way from the cutin layers. It is easier to saponify the cutin, 

 or the suberin (Karrer, Peyer and Zegar, 1923; M. Meyer, 1958) 

 and to hberate the cellulose. 



The scheme shows the relative positions of the four cell wall 

 substances, not their quantitative proportions, these being very 

 variable. Small or larger amounts of the carbohydrate wall substances, 

 cellulose and pectins can always be identified in the inner regions of 

 the cuticular layer; they are, indeed, often quite prominent. Further 

 out, it is the waxes which are in greater prominence, with marked 

 and sometimes complete decUne of cellulose and pectins. The outer 

 layers probably consist of cutin and wax only. This is noteworthy as 

 compared with lignin deposition, since cutin can obviously occur as 

 an independent wall substance, whereas lignin is always found in 

 company with cellulose. Finally, there are no waxes in the isotropic 

 cuticle (Priestley, 1943), which, therefore, comprises only a thin 

 pellicle of almost amorphous cutin. 



It would be interesting to discover the still quite unknown history 

 of the development of this complicated submicroscopic system 

 originating in a region remote from the protoplasm. Martens (1934) 

 states that the cuticle is secreted in the fluid state and then coagulates 

 in the air. This may also safely be said to apply to the cuticular layers. 

 The cutinic acids would then be dissolved in a low molecular state, 

 migrate into the wall and there polymerize. It is less difficult to under- 

 stand the deposition of the low-molecular waxes, though even in this 

 case it is necessary to assume that there is some special solvent, or 

 that unesterified wax acids and alcohols migrate. This process is 

 similar in nature to the excretion of waxes through the epidermis, 

 where they form a granular, rod-shaped or scaly coating (Weber, 

 1942). 



Each component of the wall in the full-grown cuticular layer has 

 its particular physiological function. By reason of its hydrophobic 

 nature, the primary duty of the wax is to make these layers watertight. 

 The cutin has a similar purpose, though in a less extreme degree, since 

 its hydrophilic groups make it less hydrophobic and, therefore, it has 



