BOTANICAL TECHNIQUE 633 



[Zeit. wiss. Mik., xxv, 1909, p. 29). Fix the fibres in a wire frame 

 and wet them out with alcohol. Place in a dilute syrupy solution 

 of celloidin in alcohol ether and allow to evaporate to half volume. 

 Then ])laee fibres, after gently squeezing, in a chloroform solution 

 of paraflin wax for two hours. Cut from frame, place in paraffin 

 and quickly imbed. Section at once. 



Kisser and Anderson's modification {Amer. Journ. Bot., xv, 

 1928, p. 437) has several advantages. Very thin sections in any 

 desired plane can be cut. Stain the fibres with carmalum and 

 wash in water, then stretch them as much as possible and dry 

 them between filter paper with light pressure. While stretched, 

 cement them with gum arable by their ends over a central window 

 1 cm. square, with the aid of small strips of cardboard. When the 

 gum is dry, imbed the whole frame in celloidin and then cautiously 

 cut out the central square of celloidin containing the fibre. Harden 

 this in chloroform and imbed in paraffin of 52° C. melting point. 

 To cut the suitably orientated block, wet the knife with water 

 containing 0-1 to 0-5 per cent, gelatin or soap to reduce surface 

 tension. Cross sections down to 2 /x. and longitudinal sections 

 down to 4 /i. have been obtained. Such thin sections may be used 

 for X-ray studies of the cell wall. Affix with albumen and remove 

 the paraffin and celloidin with xylol and ether respectively. 

 Make mounts in glycerin or glycerin jelly. 



1259. Chemical Sectioning of Fibres. Boil the fibre in sulphuric 

 acid and, without washing, dry in an oven until it commences to 

 char. Then mount in caustic soda and submit to suitable pressure. 

 The fibre bundles segment into transverse sections, usually 

 between 10 and 20 /a thick, quite flat, exactly transverse and 

 retaining all the fine details of structure of the untreated fibre. 

 The method is a valuable aid to the routine identification of fibres. 

 See Kelaney and Searle, Proc. Roy. Soc. Lond., B, evi, 1930, 

 p. 357. 



1260. Serial Section Mounting. Ribbons or individual sections 

 are most easily handled with the aid of a scalpel, the tip of which is 

 wetted with water. 



Paraffin Sections. The albumen and water method of Henneguy 

 is most generally used. For difficult material (moss archegonia, 

 moss capsules, grass leaves, and large sections) use one of the 

 following : — 



Land's Affixative {Bot. Gaz., lix, 1915, p. 398). Make a 1 per 

 cent, solution of gum arabic in water. Make a potassium bichro- 

 mate solution immediately before use, adding enough to turn 

 the water pale yellow (about 0-2 per cent.). Smear a few drops 

 of gum arabic solution on the slide and flood with bichromate. 

 After stretching the ribbons, drain off excess water and allow the 

 slide to dry in the light. Exposure to light renders the gum 

 arabic insoluble in water. A mixture of gum arabic solution and 



