88 METHODS IN PLANT HISTOLOGY 



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 ad- 

 justed? How is the object clamp raised and lowered? How is the 

 thickness of the section determined? In case of a simple microtome 

 like the one shown in Figure 2, the student should soon answer such 

 questions without any help from the instructor. In case of more com- 

 plicated 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 ^ is very thin, and 20, 30, or even 40 /x 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 di- 

 rections as explicit as possible, let us follow the processes from collect- 

 ing the material to labeling the slide. The rhizome of Pier is 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 foot in length, wrap 

 them in wet paper, and bring them into the laboratory. 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 should have been a beautiful preparation. 



While the material is still fresh and moist, cut the sections, placing 

 them in water as fast as they are cut. When through with the cutting 

 rinse the sections in water and transfer to 95 per cent alcohol, where 



