Grossenbacher Radial Growth in Trees. 67 



cells, and that they may he 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 comparativcy 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 130 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 a num., 

 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 Vitis and Robina 

 Pscudacacia 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 Vitis and he accordingly found the inner lay- 

 ers corroded and dissolved in spring. He also found the same 

 soiuticn of the inner unlignified layers in the bast fibers and 

 cortica Iparenchyma and collenchyma of Fraxmus 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. 



118 Schellenberg, H. C. Ueber Hemicellulosen als Reservestoffe bei un- 

 sern Waldbiiumen. Ber. Deut. Bot. Ges. 23: 36-45. 1905. 



