CURRENT LITERATURE. 
BOOK REVIEWS. 
Perception and propagation of stimuli in roots. 
A NEW FIELD oft research in plant eee has recently been opened 
stems. In the first of these* the author shows that there exist starch grains 
in the cells of the root caps of many roots, and in several other sensitive 
regions, These grains invariably occupy the physically lower side of the 
cells in which the lie. Most of the experiments were conducted upon the 
roots of seedlings and upon the coleoptiles of grasses. At the close of an 
experiment the organs were killed, and studied by staining and sectioning. 
The movement of the grains occupies a comparatively short time, a half hour 
being sufficient for their rearrangement in the cells of the root cap in Pisum, 
when this has been turned on one side. The grains are embedded in the 
plasma, and as they fall away from that part of the protoplasm against which 
they normally lie (z. ¢., when the organ is upright), the protoplasm on that 
side of the cell hides altered so that it stains much more deeply. If 
the organ has been so placed that when the grains come to rest they still 
lie against a part of the normally lower wall, only that part of the protoplasm 
which has been freed from them becomes altered. Cells which have been in 
an upright position, but have lost their starch, owing to the influence of a 
plaster jacket, show the same proptoplasmic thickening as those which have 
been turned so that the grains fall by gravitation away from their normal 
position. Roots so treated are found to have lost their power of geotropic 
curvature. The author suggests that this may be due to the loss of the starch. 
Also, when these roots are freed from the plaster and allowed to renew their 
growth, they regain their normal sensitiveness. The return of sensitiveness is 
accompanied by the formation of new starch grains in the root cap. Also, if 
the region containing the grains be cut away, geotropic reaction ceases for a 
time, and its return is simultaneous with the formation of new grains in the 
regenerated tissue. 
Némec is of the opinion that the stimulus for geotropic curvature is the 
change of pressure of the starch grains upon the protoplasm. These varia- 
tions in pressure are of such small magnitude, however, that it is well-nigh 
*NéEMEC, B.: Ueber die bears sprit des Schwerkraftreizes bei den Pflanzen. 
Jahrb. f. wiss. Bot. 36 : 80-178. 
Igor] 145 
