334 PHYSIOLOGY AT THE FARM. 



or mixture of principles which affords acetic acid when wood is 

 subjected to destructive distillation, since the larger the pro- 

 portion of the encrusting matter of the cells in any wood, the 

 more acid is obtained from an equal weight. This ligneous 

 matter contains a variable proportion of resinous matter, by 

 which the wood is coloured and its inflammability increased. 

 It also contains a proportion of saline matter and minute 

 quantities of compounds containing nitrogen. 



Cellular tissue is the fundamental tissue of every plant, 

 and when procured in an unmixed state its chemical com- 

 position is the same, whatever the plant by which it is fur- 

 nished. It is loose and spongy; nevertheless in the succu- 

 lent shoots of germinating seeds, and in the roots of plants 

 such as the turnip and potato, in the pith of the rush and 

 of the elder, it is porous and elastic ; in the fibres of hemp 

 and flax it is flexible and tenacious ; in the wood and branches 

 of growing trees it is compact, while it becomes dense and 

 hard in the shells of the filbert, the peach, the cocoa-nut, 

 and the phytelephas or vegetable ivory. 



Vegetable cellular tissue in its succulent forms is digestible 

 and nutritive, but when it has become compact and incrusted 

 with the ligneous deposit, as in the husks of seeds, in the hard 

 portions of stems, and in tenacious fibres like those of hemp 

 and flax, it is no longer fit to serve as nourishment to the 

 higher orders of animals. Nevertheless, it has been well re- 

 marked that even in this compact state, or in that formerly 

 termed lignine, it is an alimentary principle, and constitutes 

 the appropriate food of numerous insects and other of the lower 

 tribes of animals, such as are furnished with organs capable of 

 comminuting and reducing it to an appropriate degree of 

 softness. 



This is a subject of considerable interest, and deserving of 

 more attention than it has yet received. 



