A. Making Preparations 



I. Preservation of Material. In many cases it is possible, 

 and even preferable, to use fresh material, but it is often 

 convenient to keep it for a time, since many of the specimens 

 required are only to be obtained at certain seasons of the year : 

 the best liquid for this purpose is ordinary methylated alcohol, 

 in such quantity as completely to cover the material. It must 

 be remembered that this will extract the green colouring 

 matter (chlorophyll) from the material immersed in it, as 

 well as resin and other substances. 



II. Hardening:. For the general study of the histology of the 

 mature parts of plants, it is often unnecessary to harden them, 

 for the tissues are usually sufficiently firm to admit of their 

 being cut satisfactorily. In the case of young, or of exclusively 

 parenchymatous tissues, especially those of non-vascular plants, 

 it is necessary to harden them, and for this purpose alcohol 

 may be used. 



When it is desired to study the structure of the protoplasm, 

 and of the nucleus, special methods must be employed for 

 hardening them, or rather for fixing them as nearly as possible 

 in the condition in which they are during life. For this 

 purpose one or other of the fluids mentioned below may be 

 used. Care must be taken that the objects shall be of small 

 size, that the quantity of hardening fluid be large relatively to 

 the bulk of the object, and that the fluid have ready access to 

 all parts of it. Large objects should be cut up into pieces of 

 moderate size, so that the reagent may readily gain access to 

 all parts of the tissue. 



