SPECIAL METHODS 143 



Tissues are softened at a temperature of about 320° F., in an or- 

 dinary dental vulcanizer. The time required varies. For a three- or 

 four-year-old branch of oak, an hour is usually enough; but for a piece 

 of seasoned oak wood, the time is likely to be 4 or 5 hours. 



Brass pipe f-1 inch in diameter is cut into lengths to fit the vulcan- 

 izer, and the ends are threaded for brass caps. On one end, the cap is 

 made tight by "sweating" lead solder into the thread. The other end 

 is made tight by putting into the cap a piece of cardboard and, on top 

 of the cardboard, a circular piece of lead. The tube is then placed in a 

 vise, the water or alcohol, with the material, is put into the tube, and 

 the cap is screwed on tight with a wrench. 



After vulcanizing, the material is allowed to cool slowly, and then is 

 treated for a few days in a mixture of 2 parts water and 1 part hydro- 

 fluoric acid. Wash well, run up through the alcohols, and preserve in 

 equal parts glycerin and 95 per cent alcohol, until needed for cutting. 



By this method, Jeffrey cut transverse sections of cocoanut shells 

 and hard woods as thin as 2 or 3 fi. 



CLEARING THICK SECTIONS OR SMALL OBJECTS 



It is sometimes desirable to make very thick sections to show gener- 

 al topography rather than detail. A longitudinal section of the fully 

 grown ovule of Ginkgo or a cycad may be cut as thick as 3-5 mm. so as 

 to include the entire group of archegonia. A slab can be cut from each 

 side of the ovule with a fine saw, and a razor can be used for smoothing. 

 If the section is from fresh material it should be fixed, washed, etc., 

 with about the same periods as if it were to be imbedded in paraffin. 

 When thoroughly cleared in xylol, the section should be put into a flat 

 museum jar of suitable size and kept in xylol. Before the stony coat 

 of a cycad or Ginkgo ovule becomes too hard to cut readily with a 

 safety razor blade, the ovule should be run up to 85 per cent alcohol 

 before cutting the slabs off from the sides, because the turgidity of the 

 endosperm would cause distortion. If the base of the living ovule be 

 placed in basic fuchsin, the vascular system will be stained. Then fix in 

 alcohol and follow Gourley's method, described later in this chapter. 

 Such preparations, when cleared and placed in a smooth glass dish 

 with a light beneath, are very instructive. 



Sections of Zamia or other cycad stems, 2 mm., or even 5 mm. 

 thick, make instructive mounts, since thej^ show the peculiar course 

 of the bundles, a feature which is largely lost in thin sections. 



