BOTANICAL TECHNIQUE 629 



For other methods used in imbedding animal material see 

 §§ 173, 181. 



1249. Freezing is httle used, though it can be useful for frail 

 pathological specimens and soft or gelatinous algse and fungi. 

 Its use is absolutely essential in the histochemical study of the 

 distribution of diffusible salts. Bring fixed material into 4 per 

 cent, formalin and coat with egg albumen ; gelatin or gum 

 arabic to attach it to the carrier. Lay the sections on slides 

 coated with gelatin and cooled. Warm the slides to make the 

 sections adhere. Avoid stains likely to colour the gelatin. Refer 

 to Chapter XII. See Kisser, Zeit. wiss. Mik., Ixv, 1928, 

 p. 433 ; LiPPiNCOTT, Stain Tech., i, 1926, p. 39. 



1250. The use of Soap is advocated by Wilcox (J. Appl. Micr. 

 and Lab. Methods, i, 1898, p. 68), and Osterhout (C/w/i;. Cal. Puhl. 

 in Bot., ii, 1904, p. 87), for material that cannot be safely 

 dehydrated, e.g., alga?, mucilaginous and other delicate structures. 

 Saponify 70 cc. hot coconut oil with 38-5 c.c. of 28 per cent, 

 aqueous KOH. When firm, pulverise the product. Place material 

 in warm water and add the soap until the solution is quite con- 

 centrated. Then dry until the mass is firm enough to attach to 

 a wooden block in a sliding microtome. Attach sections to 

 albumened slides, moisten with xylol and press into contact. 

 Dissolve away the soap and warm the slide, or immerse in 96 per 

 cent, alcohol to coagulate the alcohol. 



1251. General. The use of a centrifuge to aid imbedding has 

 been advocated by Weber. Slow centrifuging does not disturb 

 the arrangement of the cell contents and is preferable to the use 

 of a vacuum pump. See Kisser, Protoplasma, iii, 1928, p. 507. 



1252. Sectioning of Woods and other Hard Objects. This 

 requires powerful apparatus, grinding methods or a method of 

 softening the hard tissues. Soft woods and the alburnum of harder 

 woods can usually be cut by means of a heavily built sliding 

 microtome. Thomson {Bot. Gaz., 1, 1910, p. 148) describes a 

 modified Jung-Thoma microtome for hard woods. See also Jane 

 {Ann. Bot., xlix, 1935, p. 398) for a device for the setting of 

 knives. 



A heavy steel plane with a blade of hard temper and a sharp 

 straight edge is employed to obtain fairly thin large sections. 

 The stony tissues of seeds and fruits may be sectioned by a 

 grinding process. Cut thin sections with a fine saw and grind 

 them down with fine, wetted carborundum powder on a piece of 

 plate glass. At first carry out the rubbing down with the finger 

 on the section ; when the section has become quite thin (less 

 than I mm.) use a piece of plate glass. When grinding is complete, 

 wash the section, dehydrate, clear and mount in thick, warm 

 balsam. The thin sections can be stained, but the structure 

 usually shows well in unstained mounts. 



