114 BOTANICAL GAZETTE | aueus 
hands almost as strongly as it does in the opposite direction when 
dried. 
The minute structure of the awn furnishes an explanation of the 
phenomena here described. A thorough investigation of this subject 
was made by A. Zimmerman* whose purpose was to gain a more acti: 
rate insight into the torsion mechanism of the awns of wild grass 
He gives Hildebrand credit for first attempting to explain mechan 
ically the hygroscopic torsion. His explanation was considered 
incorrect, and was not in accordance with the views of Nageli and 
Schwendener, who held that the seat of the mechanism is in the ind: 
vidual cell. Francis Darwin afterward confirmed this view. Zimmer 
mann found that in the awn of Avena sterilis (with which, he sajs 
” . a * fi ed 
the twisting power is connt 
ment. Both the arrangement of the pits in the walls of these cells and 
The present observations confirm those of others in locating es 
cause of the twisting of the awn in the individual cells and show ’ : 
not only a layer of cells but all of the mechanical cells are active im ~ 
ing about this result. . 
As is well known, the twisted portion of the awn is composed a 
cipally of sclerenchyma cells with a fibro-vascular bundle in the el 
and a band of chlorophyll bearing tissue on each side (/ig- 1). be 
latter, however, has nothing to do with the torsion. A_ striking pe 
larity of the mechanical cells is the narrowness and eccentricity of - 
lumina ; furthermore, this eccentricity in all the cells is alike, 8° = 
the lumina lie nearest the center of the awn (see figs. 7 and 3): a 
id 
Strong Schultz’s solution shows that the material imm 
around each lumen is stil] very much like cellulose; that it swells 
contracts more than the outer and denser layers of the cell wall 8 
dent, since the surface of a cross section of a single cell . 
potash is convex, but when washed and dried is concave. 
* Jahrbiicher fiir wissenschaftl. Bot. 7+ 542. 
