polysaccharides and are collectively termed holocellulose. To- 
gether with lignin, these macromolecules account for more 
than 95 per cent of the total weight of moisture-free wood 
(Table I.). Of the three, cellulose is the dominant constitutuent 
in both softwoods and hardwoods, generally averaging be- 
tween 40 and 50 per cent. Hemicellulose is usually more abun- 
dant than lignin in hardwoods whereas in softwoods, the re- 
verse is often true. Together, in both kinds of wood, they 
constitute roughly half of the total dry wood weight. All other 
wood components collectively average generally less than 5 
per cent. Among the many minor components are pectic sub- 
stances, proteins, starch, polyphenolic compounds, aliphatic 
acids, and inorganic salts. 
Cellulose provides the framework of wood structure. During 
tissue growth, lignin and hemicellulose are deposited in inti- 
mate association with the cellulosic framework as an incrust- 
ing, interpenetrating enmeshing matrix material. Because of 
this intimate association, it is not yet possible to chemically 
separate these components entirely from one another without 
affecting some alteration or modification in their molecular 
structures. 
TABLE I. 
Percentages (of total wood weight) of Major Components in 
Wood of Representative Angiosperms (a, b, and c) and Gym- 
nosperms (d, e, and f). From Timell, in Kirk (1973). 
a bc dee f 
cellulose 42 45 Sl 4] 4] 4] 
lignin 19 22 24 ot 29 33 
hemicellulose 38 29 23 31 2) 23 
total of above 99 96 98 99 97 97 
a. Betula papyrifer 
b. Fagus grandifolia 
c. Ulmus americana 
d. Picea glauca 
e. Pinus strobus 
f. Tsuga canadensis 
D4 
a 
