APPARATUS AND METHODS. 9 



(12) Two wash-bottles, one for 50 per cent, alcohol (methy- 

 lated spirit diluted with equal volume of water), the other 

 for water. 



(13) A bundle of dried Elder-pith for section-cutting. 



(14) Razors, including at least one thoroughly good hollow- 

 ground razor see 10. 



Various other articles and reagents are required for special pur- 

 poses ; these are referred to in the text see also Appendix and 

 Index. 



8. Fixation and Preservation of Material. In all 



cases fresh material should be used, both for the mounting 

 of entire specimens and for section- cut ting at least as a 

 preliminary to the examination of material preserved in 

 alcohol or treated with various reagents or stained with 

 dyes. Such specimens as starch-grains, filamentous Algae 

 (e.g. Spirogyra), leaves of Mosses, etc., which do not require 

 to be sectioned, are simply mounted in water for examina- 

 tion. 



Where thin sections must be taken, as in the investiga- 

 tion of solid organs (stems, roots, etc.), it is often an advan- 

 tage to use material preserved in alcohol, since this reagent 

 drives out air-bubbles besides rendering the tissue more 

 readily cut; but it must not be forgotten that alcohol 

 dissolves out such cell-contents as chlorophyll, oil, resin, 

 etc., and it is therefore necessary to examine fresh material 

 first whenever possible. 



If plant tissues are placed in ordinary (methylated) 

 alcohol, this reagent may cause plasmolysis of the cells. 

 For rough purposes this is no great disadvantage, but 

 even for the simple freehand sectioning, with which alone 

 we are concerned here, it is much better to be able to see 

 more in a section than a network of cell-walls and here and 

 there the shrunken and disorganised cell-contents. If we 

 wish to see the cells in something like their living condi- 

 tion, we must use reagents which will kill the protoplasm 

 rapidly and fix it and the other contents of living cells in 

 as nearly as possible the natural condition apart from 

 their having been killed. 



Various killing and fixing reagents are used for fine work, 

 or for precise staining and double staining, but for general 



