BOTANICAL MICROTECHNIQUE. 



I. The various Methods, in general. 



a. Fixing Methods. 

 a. Alcohol, C 3 H S OH. 



300. Exposure for 24 hours is usually sufficient for fixing- 

 nuclei, but a longer action does no harm. 



If one desires to prepare sections free-hand from alcoholic 

 material, it is often useful to place the material for 24 hours 

 previously in a mixture of equal volumes of alcohol and 

 glycerine, or of alcohol, glycerine, and water, which makes 

 them much better adapted to cutting. 



Concerning the addition of sulphurous acid to such prep- 

 arations as blacken in pure alcohol, see 34. 



ft. Iodine. 



301. Iodine has been chiefly used for fixing in an aqueous 

 solution of iodine and potassium iodide. Berthold (II, 704, 

 note) recommends for marine algae a concentrated solution 

 of iodine in sea-water, which may be prepared by the addi- 

 tion of a few drops of alcoholic iodine solution to pure sea- 

 water. According to Berthold, it is sufficient to move the 

 algae about in this fluid from half a minute to a minute. 

 They are then transferred directly to 50$ alcohol and, if 

 this fluid be changed a few times, can be placed in the 

 staining fluid in a few minutes. 



Overton (I, 530) has used the vapor of iodine, which may 

 easily be obtained by warming iodine-crystals in a narrow 

 test-tube, for fixing, with the advantage that they may be 

 entirely expelled by gentle warming (to 30 or 40 C.) and 

 require no washing out of the fixing medium. Their use is 

 especially to be recommended for small objects (cf. 40). 



y. Bromine and Chlorine. 



302. The vapor of bromine is recommended by Stras- 

 burger (I, 399) for fixing Fucus. [Zimmermann (VIII) 

 recommends chlorine gas for fixing such algae as Cladophora 

 and Zygnema without contraction of the protoplasm.] 



