84 
METHODS IN PLANT HISTOLOGY 
razor may hold its edge for hundreds of sections. Those sections 
which seem to be worth further treatment should be placed at once 
in water or in a fixing agent and, of course, the choice of a fixing 
agent should be determined before the sections are cut. 
With the advent of a cheap, efficient sliding microtome, the hand 
microtome began to fall into disuse and, today, it has almost dis¬ 
appeared. 
The sliding microtome (Fig. 2) reduces to a minimum the necessity 
for manual dexterity, but it is a more complicated machine. Study 
the various parts before you begin to cut sections. How is the knife 
adjusted? How is the object clamp raised and lowered? How is 
the thickness of the section determined ? In case of a simple micro¬ 
tome like the one shown in Figure 2, the student should soon answer 
such questions without any help from the instructor. In case of 
more complicated microtomes, a demonstration by the instructor 
will save both time and machine. 
In cutting sections of wood or herbaceous stems, the knife should 
be set obliquely so as to use as much as possible of the cutting edge. 
In most cases it is neither necessary nor desirable to cut very thin 
sections by this method; 10 ju is very thin, and 20, 30, or even 40 n 
is usually thin enough. 
Cut with a firm, even stroke, wetting both knife and object after 
every section. Use water, if the material is fresh; if preserved, 
use the preservative. Some use a brush in removing sections from 
the knife, but nothing is quite equal to one’s finger; anyone who is 
in danger of a cut while performing this act is in need of this little 
practice in manual dexterity. 
WOODY AND HERBACEOUS SECTIONS 
Safranin and Delafield’s Haematoxylin.—In order to make the 
directions as explicit as possible, let us follow the processes from 
collecting the material to labeling the slide. The rhizome of Pteris 
aquilina is a good object to begin with. Dig down carefully until 
the rhizome is exposed; then with a sharp knife cut off pieces a few 
inches in length, taking the greatest care not to strain the tissues. 
If the rhizome has been cut carelessly or pulled up, as is usually the 
case, the finished mount will show ruptures between the bundles and 
bundle sheaths, disfiguring what might have been a beautiful prep¬ 
aration. 
