24 Botanical Microtechnique 



precautions in mind the intervals can be regarded as sufficiently 

 flexible to conform to the demands of other duties. 



Isopropyl alcohol can be used in exactly the same manner as 

 ethyl alcohol. Isopropyl alcohol can be purchased without restrictions, 

 and the commercial grade can be dehydrated as described on page 29. 

 Methyl alcohol has not been used extensively for dehydrating plant 

 tissues. Its toxicity is objectionable, and the vigorous dehydrating 

 action damages delicate structures. 



Acetone is an excellent dehydrant. Its jjurchase and use present 

 no legal, administrative, or disciplinary problems, making it a desir- 

 able substitute for ethyl alcohol. Acetone is obtainable in several 

 grades, at jnices that vary widely with the cjuality and source. If 

 anhydrous acetone can be purchased in drum lots at reasonable cost, 

 only this one grade needs to be stocked and used for all the dehydrat- 

 ing grades. Acetone of good quality, but not strictly water-free, can 

 be obtained and used for the gradations, and the more expensive 

 anhydrous grade used only for the final stages in the process. 1 he 

 procedure with acetone is exactly the same as with ethyl alcohol. It 

 is permissible to change from alcohol, or a killing fluid containing 

 alcohol, to a grade of acetone having approximatel) the same water 

 concentration. 



Acetone is highly volatile, and care should be taken not to jxrmit 

 acetone to evaporate from tissues or slides during processing. 



Glycerin is used as a dehydrant, especially for algae and other 

 delicate subjects. The high boiling point of glycerin jjermits the 

 elimination of water by evaporation. Ihe slow, progressive dehydra- 

 tion prevents sudden changes of concentration and minimizes plas- 

 molysis. Material must be washed in water before using glycerin, 

 because the evaporation process obviously does not wash residual 

 reagents out of the tissues. Moderately firm tissues can be washed 

 in riuining water, but delicate materials shoidd be washed by diffu- 

 sion. Rinse the material carefully to remove the bulk of the kill- 

 ing fluid, transfer to a 2-Cjuart jar of \vater, and allow the jar to 

 stand undisturbed for 2 hr. Sijjhon off most of the water without 

 agitating the material, and refill the jar with water. Repeat the re- 

 placement of water at least twice then proceed with the <;l\cerin 

 method. 



Tiansfer the material to a large volume of a 5% solution of 

 gly((iiii in water. Use a wide-mouthed botik' oi jar and mark the 

 level of the 5% glycerin. I he xoluiue should be so gauged that after 

 the elimination of water the residual glycerin will more than cover 



