68 Wisconsin Academy of Sciences, Arts, and Letters. 
& 
son and that such an enzyme is not present or is inactive in the 
latter part of the growing period as indicated by the fact that 
hemicellulose is deposited in both the wood and bark at that 
time. Sanio 137 found that in Finns silvestris lignification did 
not occur in spring wood until after the deposition of the secon¬ 
dary thickening had been completed, that it began at the angles 
of the cells and then involved the radial walls and later the tan¬ 
gential walls. In the summer wood, however, the primary walls 
were found to have lignified before the deposition of the secon¬ 
dary thickening began, and it occurred in cells which were only 
a few removed from the cambium. The final composition of 
the cell walls of spring and summer wood seem also to differ, for 
according to Wider, 138 the walls of spring wood contain a lower 
percentage of cellulose than those of summer wood. 
If the deposition and lignification of cellulose are in any way 
dependent upon enzymotic action, there must be at least two 
enzymes concerned because the two processes appear to be inde¬ 
pendent of each other as indicated by Sanio’s observations. It 
is evident that either of the processes would necessarily impede 
or check further enlargement of cells differentiating from the 
cambium. It, therefore, appears permissible to assume that the 
enzymes involved in the solution of hemicellulose and the tardi¬ 
ness of the lignification process in spring are important factors 
in permitting the development of larger wood cells in spring 
than those produced in summer, when the cellulose dissolving 
enzymes are inactive and lignification occurs so quickly after a 
cell is formed that in some cases it takes place even before sec¬ 
ondary thickening has begun. The experiments by Jost and by 
Lutz also give support to the idea that radial growth is largely 
controlled by enzymotic activities which are somehow dependent 
upon the process of terminal elongation. Perhaps the enzymes 
concerned are liberated or activated in enlarging and bursting 
buds in different parts of trees and are carried downward in the 
metabolized food, or possibly enzymes produced in the enlarging 
buds simply initiate certain activities which are transmitted 
without the further aid of the enzymes as was assumed by 
137 Sanio, K. Anatomie der gemeinen Kiefer (Pinus silvestris L.). 
Jahrb. Wiss. Bot. 9: 66-68. 1873. 
188 1. c. 
