Grossenbacher—Radial Growth in Trees. 
67 
cells, and that they may be dissolved or converted into gum by 
enzymes. Potter 134 called attention to the presence of an inner 
cellulose layer in the xylem cells of many normal trees, and to 
its especial abundance in the wood fibers of Quercus, Fagus, 
Aesculus, Salix, Ulmus, Alnus, and Betula. He found that 
after keeping wood in water during some days cellulose linings 
became apparent in many cells in which none had been noted 
before the water treatment. 
Du Sablon 135 concluded that when starch disappears in late 
fall much of it is converted into reserve cellulose which is de¬ 
posited on the inner side of wood-cell walls. In some cases this 
lining was found to be comparativey thick and occasionally it 
even had folds extending into the lumen of cells. It is said to 
be readily soluble in dilute hydrochloric acid. 
Schellenberg 136 made a more thorough study of the deposi¬ 
tion and partial solution of hemicellulose in the wood and bark 
of trees. He found a hemicellulose lining on the walls of fibers 
in both spring and summer wood of Aesculus Hippo cast anum, 
Betula and other trees but it was not dissolved in spring. Since 
similar hemicellulose linings in the cells of the phloem and corti¬ 
cal parenchyma were found corroded in spring he concluded 
that the lining did not dissolve in the fibers because protoplasm 
was absent there. In the wood fibers of Yitis and Robina 
Pseudacacia he noted the occurrence of especially thick hemi- 
celulose layers in well matured wood and of much thinner ones 
in those of immature wood. The protoplasm remains alive in 
the wood fibers of Yitis and he accordingly found the inner lay¬ 
ers corroded and dissolved in spring. He also found the same 
solution of the inner unlignified layers in the bast fibers and 
cortica Iparenchyma and collenchyma of Fraxinus excelsior. 
Usually from a third to half of the unlignified layer in the cor¬ 
tical parenchyma is dissolved when the buds open. He was of 
the opinion that the deposition of hemicellulose in the bark 
parenchyma continues after the leaves fall. 
From these papers it is evident that a hemicellulose dissolv¬ 
ing enzyme is active during the early part of a vegetative sea- 
134 Potter, M. C. On the occurrence of cellulose in the xylem of woody 
stems. Ann. Bot. 18: 121-40. 1904. 
186 1. c. 
188 Schellenberg, H. C. Ueber Hemicellulosen als Reservestoffe bei un- 
sern Waldbaumen. Ber. Deut. Bot. Ges. 23: 36-45. 1905. 
