38 



UKACTIoN OF HOST TO PARASITIC ATTACK. 



men other substances make their appearance in the lignified 

 walls, chiefly tinctorial phlobaphenes. 



The walls of the wood-elements are, however, not lignified 

 in i he >aine extent. The primary layer of the wall is, as a 

 rule, liquified most and contains but little cellulose. In con- 

 MM|iiciice, on treatment witli lignin-solvents, it becomes first 

 dissolved while the secondary and tertiary membranes, although 

 their linnin is also partially dissolved out, remain behind as a 

 distinct framework of cellulose. With longer treatment destruc- 

 tion of the tissue proceeds till only the pure cellulose membranes 

 of the isolated cells remain. The ferments of many fungi act 

 in this way: for example Tramctcs pini, as shown in Fig. 12; 

 at ii the wall is in its normal condition, showing a primary 



Fiii. VI. Section of tracheides of pine-wood in process of dissolution by tlie 

 ferment of Trametes pint. i-J^. (After R. Hartig.) 



wall and two striated secondary membranes; at I the fungus- 

 ferment has caused a splitting of the primary wall, which 

 formerly appeared as a single layer, and the elements are 

 separating from each other ; the " filling-material " of the inter- 

 cellular spaces (under c), and the ring of lime surrounding the 

 cavity of the pit <1, remain for a longer time: the right wall 

 of the cell I consists only of cellulose, (as indicated by the 

 striation being no longer shown, although still present); in 

 the cell e the primary wall has disappeared, and the secondary 

 and tertiary membranes thin off towards / in which only 

 the ash constituents remain as fine granules, better seen in 

 Ki. 13. 



In contrast to the lignin-dissolving fungi, there are those 

 which dissolve cellulose. When wood is treated with sulphuric 



