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—Cork or Cuticular Tissue.—From the mode of formation of cork and cuticular tissues, it has been concluded that they are also modified celluloses. The aggregate ultimate composition of cork is represented by the following percentage numbers:

C	65·7
H	8·3
O	24·5
N	1·5

Cork, however, unlike the jute fibre, is by no means chemically simple, but can be resolved by the action of mere solvents into a number of proximate constituents, such as acids, a variety of fatty bodies, nitrogeneous bodies, &c.

Cuticular tissues, such as constitute the covering of fruits, are more simple in composition; the cuticle of the apple after purification, has the following percentage composition:

C	73·66
H	11·37
O	14·97

The cuticular substance of cotton, straw, esparto, &c., are doubtless similar bodies. These numbers point to a {27} remarkable similarity in composition to the fats, and, indeed, from the results of his study of this tissue, Frémy concluded that it was a fat in everything but its physical properties, of which we may mention insolubility in alcohol and in ether, and infusibility. This tissue, however, as also cork, contains a cellulose residue, which may be isolated by any of the methods of treatment given for ligno-cellulose. Under the action of boiling nitric acid these tissues are resolved into cellulose on the one hand, and a series of fatty acids or products of their decomposition, suberic and adipic acids, &c., on the other; the latter amounting in the case of cork to 40 per cent. of the weight of the substance treated. The cellulose obtained by this treatment is but 2–3 per cent.; this number, however, represents only the amount which has survived a treatment which we know to be destructive to cellulose. If, on the other hand, cork be resolved by treatment with sodium sulphite solution at 100lb. pressure, or 166° C. (331° F.), a soft mass is obtained, preserving the structural features of the original cork, until subjected to slight pressure, when it falls to a cellular mass. From this, cellulose is isolated by any of the less drastic processes above described, and is found to amount to 9–10% of the original cork. As in ligno-cellulose, we have evidence of a transition from cellulose to the tannins, so in cork and cuticular tissue we have evidence of the metamorphosis of cellulose into fats, a fact indicated in the term adipo-cellulose, which we have applied to the compound celluloses constituting these protective plant tissues. This metamorphosis is doubtless a very complex process, and would appear to involve the formation of tannins also, at least as a subsidiary result. Still, the essential feature of the change is the production of the peculiar fat-like substances which have been described; and with due regard to the limitation pointed out, the views here advanced represent the results of the investigations of the subject as far as they have proceeded.

It may be observed that the general characteristics of the {28} adipo-celluloses as of the ligno-celluloses are those of a complex aldehyde.