INTRODUCTION. 9 



parallel to or includes the long axis of the object. It is 

 evident that longitudinal sections of all cylindrical ob- 

 jects may be either radial or tangential. A radial 

 section is one lying in the plane of a radius. A tangen- 

 tial section is one parallel to a plane tangent to the 

 cylinder. 



Longitudinal sections are much more difficult to 

 make than transverse and they are nearly or quite use- 

 less unless truly longitudinal. 



The razor. The secret of making good sections 

 lies in having and keeping a sharp razor. No 

 amount of skill can make a dull razor cut a thin 

 section. 



The edge of the razor must be free from nicks. This 

 can be determined by looking at the profile of the edge 

 against a bright light with a lens. Nicks, if small, can 

 easily be taken out on a hone. 



The razor should be stropped often. It is easier to 

 keep it from getting dull than to sharpen it after it has 

 become so. If its edge is free from nicks and it will cut 

 a hair of the head 2 cm. from where it is grasped by the 

 fingers, it is in good condition. 



After using the razor be careful to see that no mois- 

 ture or plant juices are left on the blade; they will 

 surely rust it if allowed to remain. 



Holding specimens. Large specimens of which 

 sections are to be cut may easily be held in the 

 fingers. They should be held vertical, grasped 

 by the fore-finger and thumb of the left hand 

 so that the razor blade may rest on the cor- 

 ner of the fore-finger, and the remainder of the hand 

 be out of the way below. 



