§ 247. SUBERIN. 255 



The tissue of turnip, chicory-root, and elder-pith, which is 

 principally parenchymatous, yielded hardly anything to chlorine- 

 water. Pfeil also came to a similar conclusion with regard to the 

 tissue of apples.^ 



The substance formerly known as sulerin is in part the cuti- 

 cular substance just alluded to ; it should, however, be observed 

 that under this name less recent authors understood a mixture 

 of fat, wax, tannin, etc. ^ Siewef t has published a minute in- 

 vestigation of the substances that accompany suberin, but not of 

 the suberin itself ; our knowledge of that substance is but very 

 insufficient, and I can only state that it is not dissolved by the 

 usual solvents, that it is more easily attacked by certain oxidizing 

 agents than lignin, but is more difficult to remove completely by 

 digestion with chlorine-water. Nitric acid of sp. gr. 1 "3 attacks 

 it very energetically ; and with an acid of sp. gr. 1 "4 the action 

 may be so violent as to cause ignition. It resists chromic acid 

 more powerfully than lignin. Whether suberin really yields the 

 eerie and suberic acids that have been obtained by the decom- 

 position of cork is still a matter of uncertainty. 



Siewert estimates the amount of suberin in cork at 90 per 

 cent. ; but I think this is too high. I feel convinced that the 

 residue he speaks of as suberin must have contained a consider- 

 able quantity of true cellulose. (Koroll found 50 per cent, in 

 the outermost parts of birch-bark.) 



In my opinion, the hardening substance of many woody fungi 

 is possibly identical with suberin. ^ 



For the microcheniical characters of cutin, lignin, etc., see also 

 VogH andPoulsen.5 (See also § 249.) 



The remarkably constant proportion existing between the 

 amount of cellulose and lignin, etc., present in varieties of wood, 

 raises the question whether these two substances do not occur in 

 combination with one another. The attempt has frequently been 

 made to regard the substance of the cell-walls of lignified tissue 



^ Loc. cit. 



2 Compare Siewert, Zeitschr. f. d. ges. Naturw., xxx. 129; Journ. f. pract. 

 Cham. civ. 118, 1868. See also Höhnel, Sitz.-ber der phys. math. K. d. Akad. 

 d. W. in Wien, 1877 ; Bot. Ztg. 783. 



3 Compare my ' Chem. Unters, eines an Betula alba vork. Pilzes.' Diss. 

 Petersburg, 1864. 



4 Zeitsch. d. österr. Apotheker-Ver. 1867, 16, 34, 60. 

 ^ ' Botanisk Mikrokemi.' Kjöbenhavn, 1880. 



