1897] THE CURVATURE OF ROOTS 333 
with respect to the vertical, but with the excitation tending to 
induce curvature in the opposite direction. The results obtained 
from the sections of roots thus treated form by no means the 
least important part of this paper. 
XII. PREPARATION OF SECTIONS. 
In the determination of changes in the motor zone it is of 
the greatest importance to kill and fix the tissues with no dis- 
turbance of the existing relations of the membranes, and to cut 
Sections in the plane of curvature through a region embracing 
the root cap and the region lying between it and the motor zone, 
and a portion of the root basal to the motor zone. Further- 
more, it is highly desirable that the sections made under differ- 
ent conditions should be made permanent and held for 
comparison. Simple as this matter may seem, it does not 
appear to have been done by any of my predecessors. The 
roots were killed, hardened, and fixed ina 1 per cent. solution 
of chromic acid, in which they were allowed to remain for 
twenty-four hours. After careful removal from the chromic 
acid, they were placed in perforated porcelain cylinders, washed 
for twenty-four hours in running water, then successively trans- 
ferred through a series of alcohols to go per cent., and into a 
weak solution of Bismarck brown in commercial alcohol. The 
roots were allowed to remain in the stain two or three days, and 
were then washed out for twenty-four hours in absolute alcohol, 
and were transferred through mixtures of alcohol and xylol and 
paraffin into the paraffin bath at 50° C. Six hours later they 
were embedded, sections cut on a Minot microtome, fixed to the 
slide with collodion and clove oil, cleared with turpentine and 
mounted in Canada balsam in oil of cajeput. This method was 
found to give most excellent results. The walls were deeply 
Stained, while the protoplasm and nucleus took up the dye only 
Sparingly. The color is especially well adapted to photomicro- 
§raphic reproduction. 
