CHAPTER IV 

 GENERAL REMARKS ON STAINING 



Many things may be examined alive without killing, fixing, 

 staining, or any of those processes. A filament of Spirogyra shows 

 the ehromatophore nicely if merely mounted in a drop of water; 

 the nucleus may be visible and the pyrenoids can usually be located. 

 Of course, such a study is necessary if one is to understand anything 

 about the plant, and in an elementary class this might be sufficient, 

 but a drop of iodine solution applied to the edge of the cover would 

 emphasize certain details, e.g., the starch would appear blue, the 

 nucleus a light brown, and the cytoplasm a lighter brown. This 

 illustrates at least one advantage to be gained by staining ; it enables 

 us to see structures which would otherwise be invisible, or almost 



invisible. 



SELECTION OF A STAIN 



With so many stains at our disposal, it at once becomes a problem 

 just which stain or combination to use in each particular case. 

 Beautiful and instructive preparations occasionally result from some 

 happy chance, but uniform success demands skill and judgment in 

 manipulation, and also a knowledge of the structures which are to 

 be differentiated. Let us take a vascular bundle for illustration. 

 Safranin stains the xylem a bright red, but, with judicious washing, 

 is entirely removed from the cambium and cellulose elements of the 

 phloem. A careful staining with Delafield's haematoxylin now gives 

 a rich purple color to the cellulose elements which were left unstained 

 by the safranin, thus contrasting sharply with the lignified elements. 

 If cyanin and erythrosin be used, the xylem takes the blue while the 

 cambium and phloem take the red. 



The mere selection of two colors which contrast well is not 

 sufficient. Green and red contrast well, but safranin and iodine 

 green would be a poor combination, for both would stain chromo- 

 somes and neither would stain the spindle; both would stain lignified 



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