STUDIES ON THE LIGNIN AND CELLULOSE OF woop. 45 
Cellulose is said to occur in two ways in the fibers of 
wood in tree stems:* much more commonly as an inner, 
lining layer sometimes completely filling the cell lumen; 
and much more rarely as a layer situated between other 
lignified ones. Personal examinations have shown it to 
occur, with few exceptions, as an inner, supernumerary 
layer, but it has also been found that in exceptional cases 
nearly the whole secondary layer of the wall, which is 
usually completely lignified, gives a cellulose reaction 
although the reaction is more marked as we pass from the 
middle lamella to the cell lumen. 
In the first lot of samples used for the preliminary tests 
it was found that cellulose occurred only in the wood of 
Populus tremuloides from New Mexico and in the wood 
of several trees of Larix Americana from the same local- 
ity in Michigan. In both cases the cellulose occurred only 
in some of the wood fibers and was present in the form of 
a lining, supernumerary layer of the wall. 
In the more extended examinations made later cellulose 
was found in the wood of Populus balsamifera from the 
same locality as were the above mentioned trees of Larix 
Americana from Michigan. It may be added that a tree 
of Populus tremuloides from Vermont also showed large 
quantities of cellulose in the wood fibers. The occurrence 
of cellulose so markedly in all of the specimens of Populus 
wood available led to the suspicion that the species of the 
genus Populus might be characterized by this phenomenon 
wherever they might grow. Accordingly an effort has 
been made to obtain, as far as possible, specimens of all 
of the native species of this country. Of the eleven 
species which are listed by Sargent f in his latest publica- 
tion the following have been examined: Populus tremu- 
loides, Populus balsamifera, Populus deltoidea, Populus 
trichocarpa and Populus acuminata. Every specimen 
* Sanio. Bot. Zeitung. 1868 ; 101-111. ¢ Sargent. 1. ¢. 
