38 THE VEGETABLE CELL IK GE^BBAL. 



any marked advantage over tliat -whlcli gives nearly the saiae 

 color, namely, phloroglucin. 



155. By the employment of these reagents many cell-walls 

 have been shown to be distinctly lignifled when the older re- 

 agent — iodine in solution — failed to detect the change \ 



156. Cutinization. Ordinary and lignifled cell-walls, a>\d those 

 which have undergone the mucilaginous ma|i|||^Q, absorb 

 water freely. On the other hand, the walls of ^^^^HKlS found 

 chiefly on the exterior of organs are repellentl^HP^Lstance 

 which imparts the repellent character to the cel^Kl^is .nJ*^°o^° 

 as cutin ; when restricted to cork it is called sub^t -■ 



157. Cutin and suberin have been described a^ifferen t sub- 

 stances ; but although the former is more generalh/associat'sd wWii*. 

 waxy matters, its reactions are essentiallj- the same as' yhose of 

 suberin. The water-prooflng of the cell-wall maj^ be superficial, 

 as in most joung epidermal cells, or it may afl"ect the whole 

 structure of the wall, as in the case of cork. If a distinction is 

 made between the two states, the first maj- be termed cutiniza- 

 tion, the second, suberification. 



158. Cutin can be removed from the walls with which it is 

 associated, by the use of Schulze's macerating liquid, subsequent 

 treatment with potassa, and careful washing. It is sometimes 

 necessary- to heat the section in potassa before the cellulose can 

 be completely freed from the other matters. 



159. Hohnel' has shown that the wall of a cork-cell, with 

 the exception of the 3'ouDg cork-cells in Coniferse, is composed of 

 five plates: (1) a middle plate, common to the tvro contiguous 

 cells; (2) two plates, one on each side of the latter, consisting 

 of cellulose which is both cutinized and lignifled ; (3) two plates 

 of cellulose forming the inner lining of the respective cells. The 

 latter plates may be more or less lignifled. Differences in the 

 relative proportions of these constituent plates give rise to dif- 

 ferences in the character of different kinds of cork. 



160. As in the case of lignin, the diflflculty of extracting cutin 

 renders its chemical composition doubtful. It is usually given 

 as follows : — 



Carbon 73-74 per cent. 



Hydrogen 10 " 



Oxygen 17-16 " 



But there is also a trace of nitrogenous matter demonstrable ; 

 this probably belongs to residual protein matters which are in 



1 Sitzungsber. d. k. Akad. Wien, Bd. lx.xvi. 1 Abth. 



