_General conclusions._—The aldehydic character of the group of ligno-celluloses is typical of the constituents of plant tissues generally, and is, there can be no doubt, extended to the celluloses. Indeed the evidence of biological observation goes to show that the ligno-celluloses are formed, by a process of chemical modification, from some more purely cellulosic tissue, which preceded it, and with this modification there is, nevertheless, a retention of the general features of the original cellulose. In the domain of animal chemistry, recent investigation has also shown that the development of proteid tissues finds its chemical expression in their aldehydic characteristics, or as it has been put, the immediate physical cause of life is to be found in the _chemical tension_ of aldehydes. The meaning of this expression will be readily grasped on {26} reference to the properties of the aldehydes as a group; their power of combining with oxygen; of uniting by their own molecules, to polymerise; of uniting by way of dehydration; of combining with the aromatic alcohols; a consensus of properties which shows them to possess an activity surpassing that of any other group of compounds. The evidence of biology, added to our knowledge of the properties of these substances, would lead us therefore to define cellulose as a condensed aldehyde allied to the sugars, and likewise containing alcoholic OH groups; and ligno-cellulose a compound cellulose, containing a cellulose nucleus or residue so combined with certain groups which may be included in the term _non-cellulose_, that it yields, under the action of reagents, products belonging either to the aromatic, the furfural, or the fatty group. _Adipo-cellulose._—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