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STUDIES ON THE LIGNIN AND CELLULOSE OF woop. 5l 
supernumerary, lining layer of the fiber walls has been held 
by several boganists to be due to arrested development of 
the walls. It has seemed to the writer that there are 
certain facts in connection with cellulose thus situated 
which point directly against this theory. First, cellulose 
as above mentioned forms an extra layer of the wall. In 
other words the wall is completely formed and has, besides 
the usual layers, an extra one consisting of cellulose. 
Measurements of the fiber walls of Populus balsamifera 
show a difference of five microns in favor of the walls 
having the cellulose layer, over those which do not have ~ 
that layer. Second, the wall with the cellulose layer is 
thicker than that without the cellulose, as is shown by the - 
above measurements. It may also be stated that the dif- 
ference in most of the woods was striking enough so that 
the observer could easily perceive without measuring that 
there was a decided difference between the two kinds of 
walls. Third, those fibers which are situated near vessels 
or tracheids do not usually have the cellulose layer. That 
is, those fibers which commonly do not have starch depos- 
ited within them are the ones which seem to be more apt to 
have the cellulose. This might be connected with the con- 
version of the starch into cellulose in such of the fibers as 
do not have the starch. Sablon* has proved that in willow 
wood the cellulose is plentiful when the starch has disap- 
peared almost completely, and there thus seems to be a 
direct conversion of the starch into the cellulose. _ Fourth, 
the tendency is for the cellulose to be present in the spring 
wood and not in the summer wood of the annual ring 
where it would seem that arrested development would be 
most apt to affect the formation of the wall. There has 
been noted no indication of the final lignification of this 
cellulose layer, although Sanio f has stated that he noted such 
* Sablon. Revue générale de Botanique. 16: 362. (1904). 
+ Sanio. 1. c. 
