630 BOTANICAL TECHNIQUE 



Seeds with a reserve of hard celhilose are usually softened 

 sufficiently by boiling in water. 



1253. Demineralisation by means of hydrofluoric acid usually 

 brings about considerable softening. This removes silica com- 

 pletely, has little effect upon the middle lamella and leaves the 

 coarse contents intact. Kerr {Trop. Woods, xl, 1934, p. 37) 

 states that softening by HF is associated with partial degradation 

 of cellulose and the formation of hydroceilulose ; softening is 

 correlated with a loss of tensile strength of the cellulose. The 

 blocks of wood for treatment should be cut to expose true trans- 

 verse, radial, and tangential surfaces. Brown {Bull. Torrey 

 Bot. Club., xlvi, 1919, p. 127) suggests 2 cm. radial length, 8 mm. 

 vertical height, and a tangential width of 6 mm. Occasional 

 species require blocks of different, or larger, dimensions to display 

 higher rays or other special features. The blocks should be 

 marked with numbers for record and with arrows to indicate the 

 direction of growth. 



Boil the specimens, dry or fresh, in water and exhaust under a 

 vacuum pump to free them of air. Brown removes the air by 

 alternate boiling and cooling. Soak in HF (full strength or 

 diluted) for one to several weeks, changing the liquid occasion- 

 ally. When maximum softness has been attained (found by 

 testing with a knife), wash out the acid by washing four days in 

 running water, and soak the blocks in glycerin. Imbed if neces- 

 sary ; celloidin is usually recommended ; adopt a rapid method 

 if possible. 



Langdon {Bot. Gaz., Ixx, 1920, p. 82) describes the action 

 of HF (both pure and diluted) on lignified structures, and pays 

 especial attention to the time of immersion of tissues in the 

 acid. She imbeds in paraffin : dehydrate with alcohols (five 

 grades : 60, 70, 80, 95 and 100 per cent, for twelve hours each) 

 after soaking several days or weeks in equal parts of glycerin 

 and 30 per cent, alcohol (Langdon, Bot. Gaz., Ixv, 1918, p. 313), 

 and clear in xylol (four grades, twelve to twenty-four hours each). 

 Remove any air or gases remaining by means of a vacuum pump 

 when the material is in pure xylol. Infiltrate thoroughly with 

 paraffin and section on a sliding microtome. A rotary microtome 

 can be used if the objects are small and have much soft tissue. 



Jeffrey {Anatomy of Woody Plants) after HF treatment 

 soaks blocks of uniform texture in a mixture of equal parts of 

 glycerin and 30 per cent, alcohol ; those of some size or hetero- 

 geneous texture in equal parts of glycerin and 90 per cent, 

 alcohol. 



Lek {Landbouwhogesch. Wageningen, Lab. Tiiinbouwplantenteelt, 

 1928 (5), p.l) shortens the process of demineralising hard tissues 

 to one or two days by heating for one hour in an autoclave at 

 16° C, using full strength HF. 



