(a) GENERAL TREATMENT OF TISSUES 



Material must be killed and fixed immediately it is collected to 

 ensure that tissues are preserved with as life-like an appearance 

 as possible. 



Small organisms such as unicellular algae, filamentous fungi, 

 etc., may be placed directly into the killing fluid. Large objects 

 must be cut at once into pieces not exceeding 5 mm. in any one 

 direction, and care must be taken to avoid rough handling and 

 pressure. 



There are a great number of killing and fixing fluids to choose 

 from and the reader should refer to the chapter on fixatives in this 

 book as well as to standard text-books on botany such as Johansen 

 or Chamberlain. The best general killing fluid, however, is 70% 

 alcohol containing o-i% glacial acetic acid; material should be 

 immersed in this fluid from ten minutes to an hour. 



After killing and fixing, material may be preserved, if it is not 

 required for immediate examination, in 70% alcohol containing 

 20% glycerine, or in 10% formalin buffered to pH 7-0. 



Delicate material should be stored in 85% alcohol containing 

 20 ml. glycerine per 100 ml. while tough hard material is best stored 

 in 50% alcohol containing 20 ml. glycerine per 100 ml., but here 

 again the reader is referred to standard text-books on botanical 

 technique. 



Material taken from the fixing and killing fluid or from the 

 preserving fluid should be washed well in running water. Tissues 

 may be dehydrated, cleared and embedded, as in the case of animal 

 tissues. Alternatively, sections may be cut, without dehydration, 

 clearing and embedding, either by means of a hand microtome, 

 or by placing thin slices of the material in a slit cut in a piece of 

 elder pith and cutting sections " freehand '* with the razor edge 

 facing away from the operator. In cutting freehand sections, the 

 razor should be kept wet with 10% aqueous glycerine. 



Glycerine (pure or diluted with water), or glycerine jelly should 

 be employed for mounting temporary preparations after staining, 

 while the preparation of permanent slides may be carried out in 



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