132 BROWN: Woops FOR MICROSCOPIC STUDY 
of the hanging type should not be used in that it tends to round 
the planes of the knife wedge. The wedge angle is best regulated 
by the use of a cylindrical metal clamp fastened to the back of the 
knife during the process of sharpening. 
In addition to the possession of (1) true axial alignment , the 
edge should (2) be sharp enough throughout its length to cut a hair 
7 
t 
Tt 

tdeediee el ee  en 
Fic. 2. Block showing tropical wood (Te- 
coma sp.) with tissues properly oriented for 
sectioning in cross, radial, or tangential planes. 
heart-wood; S, sap-wood. The rays (M, 
R) are low and narrow; the vessels (V), num- 
erous and small. G, growth-ring. 
at least one full growth-ring (G, Fic. 
by contact and (3) should 
appear perfect'y even and 
without nicks under the low 
power of the microscope. 
The number of sections 
which may be cut without 
re-sharpening the knife is 
ordinarily small; with diffi- 
cult material, frequently as 
few as two or three perfect 
sections. 
3. PREPARATION OF 
MATERIAL FOR 
SECTIONING 
A. CUTTING THE BLOCKS 
In preparing material 
for sectioning, the blocks 
must be shaped with refer- 
ence to the plane or planes 
in which the sections are to 
be cut. Thus a block in- 
tended for a cross, radial, 
and tangential series of 
sections may have a radial 
length of 2 cm., a vertical 
height of 8 mm., and a 
tangential thickness of 6 
mm. Sections cut from 
the three planes of such a 
block will ordinarily include 
2) and the full height of the 
