48 ANATOMY OF THE GYMNOSPERMS 



various modifications which may all be embraced under the com- 

 prehensive term lignin. Such lignification is, in general terms, 

 characteristic of the woody tissue of all plants in various degrees, 

 but usually in such manner that the hardness of the parts is 

 directly related to the extent of lignification. The differences 

 thus briefly indicated not only bear an important relation to the 

 action of various chemical reagents and stains, but they are 

 of the first importance in explaining the variable phenomena of 

 decay ; since it is found that neither chemical agents, stains, nor 

 decay act uniformly upon all parts of the cell wall, their action 

 varying according to locality as well as according to the particular 

 agent or the specific organism concerned. It will therefore be 

 profitable to inquire somewhat more closely into these relations. 



According to Weiss (75, 61) the percentage composition of 

 the unaltered cellulose may be taken as C 44 4 H 6 . 18 O 49 38 . In the 

 course of growth, however, alterations of various kinds arise 

 through the introduction of carbohydrate bodies of various kinds, 

 though all belonging to the cellulose group, so that the com- 

 position can no longer be represented by such a simple formula 

 as that given. The composition of these secondary products or 

 incrusting substances, though somewhat widely different in dif- 

 ferent plants, may be said to vary within an approximate percent- 

 age range of 5.99 for carbon, 0.53 for hydrogen, and 8.15 for 

 oxygen, while their mean composition may be stated as C 50.7, 

 H 6.08, O 43.03 per cent. On the other hand, the incrustation 

 substance from the same plant (Fagus sylvatica) may be found to 

 vary from C 48. 10, H 6.09, O 47.81 per cent to C 67.91, H 6.89, 

 O 25.20 per cent. A comparison of these modified forms with 

 normal cellulose brings out the important fact that while there is 

 essentially no change in the percentage proportion of hydrogen, 

 the oxygen has been reduced in varying quantities from 1.57 

 per cent to 24.18 per cent with a corresponding increase in the 

 relative proportion of carbon. 



Accompanying changes of the nature thus far discussed - 

 the formation of the secondary wall and the deposition of lignin 

 substance - - are always associated with the deposition of mineral 



