BROWN: Woops FOR MICROSCOPIC STUDY 129 
The writer is indebted to Professors J. W. Toumey, S. J. 
Record and others, of the Yale School of Forestry, and to Pro- 
fessors A. W. Evans and G. E. Nichols, of the Department of 
Botany, for the use of authentic material, for the facilities essen- 
tial for accurate work, and for many helpful suggestions and 
criticisms. 
2. ADJUSTMENT OF MICROTOME 
For sectioning, Thomson’s modification of the Jung-Thoma 
sliding microtome (’10), supplied with Walb blades 170 mm. in 
length and 35 mm. in width, was used. To secure the best results, 
it was found essential that careful attention be paid both to the 
sharpening of the knife and to its adjustment on the carriage of the 
microtome. Briefly, the knife was first sharpened to a wedge- 
shaped edge of which the two planes were inclined at an angle 6 
(Fic. 1) of 20° to each other. At the same time, perfect axial 



Fic. 1. Diagram to show edge of sliding microtome knife cutting section 10 ¢ 
thick. § (representing downward inclination) = 4.° @ (representing acuteness of 
edge after being ground with back raised by cylindrical clamp) = 20. 
alignment of the cutting edge was secured in the manner to be 
described presently. In mounting on the carriage, the blade 
was first inclined downward so as to form an angle 6 (Fic. 1) of 4° 
between the lower plane (OC) of the knife wedge and OE, the 
plane in which a given tissue is to be sectioned (vertical incli- 
nation). The knife carriage was then revolved in a horizontal 
