SPECIAL METHODS. 149 



researches of Gilson (I) have made it at least very question- 

 able if there is any cellulose present in suberized walls. 

 This author isolated from the cork of various plants an acid r 

 pliellonic acid, which, as well as its potassium salt, becomes 

 rose- or copper-red with chloroiodide of zinc. Gilson be- 

 lieves that the cause of the violet or rather reddish color 

 which these membranes treated with caustic potash assume 

 with chloroi'odide of zinc is to be sought in the presence of 

 potassium phellonate. In fact, the staining described does 

 not appear if the walls are extracted with boiling alcohol 

 after treatment with caustic potash, and before the addition 

 of the chloroiodide. The color which appears after prelimi- 

 nary treatment with chromic acid is probably due, according 

 to Gilson, to the formation of free phellonic acid. The 

 absence of color after treatment with cuprammonia is due, 

 not to the solution of cellulose, but to the conversion of 

 potassium phellonate into the copper salt, which takes a 

 yellowish-brown, very slightly characteristic color with chlo- 

 roiodide of zinc. Finally, the presence of cellulose in the 

 suberized wall is rendered improbable by the fact that the 

 whole suberin lamella may be made to disappear, according 

 to Gilson, by long continued treatment with a 3$ boiling 

 alcoholic solution of potassium hydrate, which does not 

 recognizably attack cellulose. 



263. Besides phellonic acid, already described, to which 

 Gilson assigns the formula C 92 H 43 O 3 , two other acids have 

 been isolated from the cork of Quercus Suber by the same 

 author, suberic acid (C 17 H 30 O 3 ) <md phloionic acid (C n H 21 O 4 ?). 

 It still remains undetermined in what form these acids are 

 Contained in suberized membranes. But it is not probable 

 that they occur as true glycerine ethers, since the suberin 

 lamella is insoluble in all solvents for fats and could not be 

 melted by Gilson when heated up to 290 C. The view sug- 

 gested by Kugeler (I, 44) that suberin is so difficult of solu- 

 tion because the suberin molecules are enclosed between 

 cellulose molecules is untenable, since it is shown that the 

 suberin lamella contains, at most, only traces of cellulose. 

 Therefore, at present, Gilson's view that suberin consists 



