78 Cellulose 



which remain intimately associated with the cellulose, of the 

 cell or fibre in combination, as a compound cellulose, there- 

 fore (lignocellulose, see p. 137). These derived celluloses 

 exhibit a close general conformity with the parent type that 

 is, apart from, or in addition to, the special properties and 

 reactions due to the presence of the hexene ring, all the typical 

 characteristics of the cellulose proper. 



Although, however, the hexene ring is thus shown to be 

 represented in compounds identified with the ' organic ' func- 

 tions of the plant cell, this does not appear to be the case with 

 the fully ' condensed ' benzene ring. Aromatic compounds are 

 formed in profusion, it is true, in the general range of plant life, 

 but when they appear it is in the unorganised form, i.e. as 

 excreted products of metabolism. The same appears also to 

 hold for the terpene series. 



It may also be noted here that the supplies of raw mate- 

 rials hydrocarbons &c. for the enormous modern industry in 

 ' aromatic ' products are derived from the products of coal 

 distillation, and therefore may be traced back to a cellulosic 

 origin. 



The Cellulose Group. Thus far we have been dealing 

 mainly with one member of the very numerous class of plant 

 constituents comprehended in the term 'cellulose.' While the 

 properties and characteristics of cotton cellulose are in such- 

 wise representative that this substance may be regarded as 

 the typical cellulose, the differentiation of this, as of every 

 other group of tissue constituents, in conformity with func- 

 tional variation, necessarily covers a wide range of divergencies. 



The celluloses of the plant world, so far as they have been 

 investigated from the point of view of chemical constitution, 

 group themselves as follows : 



(a) Those of maximum resistance to hydrolytic action, and 

 containing no directly active CO groups. 



