The Biology of Polyporus Pargamenus Fries 99 
of the cell-wall of the prosenchyma elements respond to 
lignin tests as they do in normal wood. The cells bordering 
on these elements are in various stages of decomposition. 
In some the tertiary layer no longer gives the characteristic 
color reactions when treated with various lignin reagents, 
but remains colorless. In other cells the secondary lamella 
of the cell-wall also remains colorless and undoubtedly con- 
sists of practically pure cellulose. As a general rule, both 
the secondary and tertiary layers remain in place until after 
all of the cell-wall but the middle lamella is delignified, 
whereupon the destruction of the cellulose commences. 
Those layers of the cell-walls that remained colorless after 
treatment with hgnin reagents take on a pronounced violet 
color when treated with cellulose reagents such as chlorzinc- 
iodine. Groups of these cells sometimes are seen in which 
the middle lamelle are colored brown with chlorzinc-iodine, 
while the secondary and tertiary layers are colored a deep 
violet and frequently exhibit a pronounced swelling. If 
sections are subjected to the action of chlorzinc-iodine for 
several hours, the cellulose layers swell up to such an extent 
that the cell lumina often entirely disappears. The behavior 
of these membranés with chlorzinc-iodine affords a double 
proof of theit cellulosic nature; first, by reason of the violet 
color assumed, and second, by reason of the swelling of the 
cell-membrane after the application of this reagent.*® 
It is evident from the above description that the dissolu- 
tion of the cellulose does not occur within any one cell until 
some tiine after its wall, the middle lamella excepted, has 
become completely delignified. Within the individual cell, 
the cell corners, where “the middle lamelle often are thick- 
ened characteristically, respond the longest to tests for lignin. 
Owing either to the fundamentally different composition of 
the basic principle of the middle lamella or to its subsequent 
infiltration by lignin constituents, it resists decay longer than 
* This swelling of decaying membranes is too often attributed to the 
action of the fungus effecting the decay. As a general rule, the swelling 
does not occur until after the application of chlorzine-iodine, and the 
swelling is to be attributed to the action on the cellulose of the excess 
zine chloride found in this reagent. 
