The Typical Cellulose and the Cellulose Group 67 



in a warm place (35-45). In the course of a week or so the paren- 

 chymatous tissue is so far broken down and gelatinised that it is 

 easily detached from the ' skeleton tissue ' constituting the vena- 

 tion of the leaf. This is a cellulose, or rather lignocellulose (see 

 p. 92), of the more resistant type ; and the process affords a simple 

 means of differentiating the cellulose group in regard to resist- 

 ance to hydrolytic agencies. 



The 'rot-steep' or retting of flax is another important illus- 

 tration. The separation of the bast fibres of the plant from the 

 cuticular tissues on the one side, and the woody stem on the other, 

 is greatly facilitated by the breaking down of the parenchymatous 

 tissue with which the bast cells are in contact ; it is this tissue 

 which rapidly ' rots ' under the treatment, and the process is 

 another illustration of ' natural ' differentiation of cellulosic tissues. 



The third group of decompositions involves the much 

 debated question of the 'fate ' of cellulosic tissues in their passage 

 through the alimentary canals of animals, or, to put it more 

 narrowly, the feeding or nutritive value of cellulose. We may 

 take it that the typical cotton cellulose would not be sensibly 

 affected by a passage through the most powerful processes of 

 animal digestion. There are, on the other hand, a number 

 of celluloses which would be, and undoubtedly are, readily 

 digested ; and the further consideration of this point may be 

 deferred until we have dealt with the specific differences 

 exhibited by the various members of the cellulose group, more 

 particularly in relation to acid and alkaline hydrolyses, under 

 which groups of decompositions the digestive processes maybe 

 generally included. 



Special mention may be made of the results of an investiga- 

 tion, by Horace Brown (J. Chem. Soc.), of the question of the 

 presence of a cellulose-dissolving enzyme in the digestive tract of 

 herbivora. After exhaustive inquiry the author establishes the 

 conclusion that the enzyme is secreted by the plants themselves, 

 and comes into activity under the favourable conditions provided 

 by the digestive organs and processes of the animal. 



F 2 



