226 Cellulose 



influences of water and unlimited atmospheric oxygen. The 

 protecting external tissues are those which we are about to 

 describe as constituting the third important group of com- 

 pound celluloses These tissues contain, in admixture with 

 the tissue-substance, a variety of oily and waxy products 

 (easily removed by mechanical solvents), the presence of which 

 adds very considerably to the water-resisting property of the 

 tissue. It will be seen as we proceed, however, that the tissue- 

 substance, after being entirely freed from these adventitious 

 constituents or oily excreta, yields a large additional quantity 

 of such products when decomposed by 'artificial' processes 

 of oxidation and saponification. By this and by its empirical 

 composition (infra) the tissue-substance will be seen to contain 

 * residues ' of high carbon percentage and molecular weight, and 

 closely allied in chemical structure to the oil and wax compounds 

 found in the ' free ' state in the tissue as it occurs in the plant. 

 These groups are associated in combination in the tissue with 

 cellulose residues, and hence the description of such complexes 

 as adipocelluloses. 



CORK in its ordinary form is a complex mixture containing 

 not only oils and waxes, but tannins, lignocelluloses, and nitro- 

 genous residues. The following are the results of elementary 

 analysis : (a) of cork purified by exhaustive treatment with 

 ether, alcohol, and water; () of cork (Quercus subcr] without 

 purification ; (c) of the cork tissue of the cuticle of the potato 

 (tuber) purified by exhaustion with alcohol. 



() (*) W 



C . . . .67-8 657 62-3 



H .... 87 8-3 7-1 



O . . . .21-2 24-5 27-6 



N .... 2-3 1-5 3-0 



The analyses are calculated on the ash-free substance 

 (Dopping, Annalen, 45, 286 ; Mitscherlich, Annalen, 75, 305). 



