68 Methods in Plant Histology 



According to Fischer (1897 and 1900), stains indicate physical 

 but not chemical composition. Fischer experimented with sub- 

 stances of known chemical composition. Egg albumin was shaken 

 until small granules were secured. These were fixed with the usual 

 fixing agents, and then stained with Delafield's haematoxylin. The 

 extremely small granules stained red, while the larger ones became 

 purple. Since the granules are all alike in chemical composition, 

 Fischer concluded that the difference in staining must be due to 

 physical differences. With safranin, followed by gentian-violet, 

 the larger granules stain red and the smaller violet; if, however, the 

 gentian-violet be used first, then treated with acid alcohol and fol- 

 lowed by safranin, the larger granules take the red and the smaller 

 the gentian- violet. In root-tips similar results were obtained. 

 Safranin followed by gentian-violet stained chromosomes red and 

 spindle fibers violet, while gentian-violet followed by safranin stained 

 the chromosomes violet and the spindle red. One often reads that 

 chromosomes owe their strong staining capacity to nuclein, and 

 especially to the phosphorous, but, according to Fischer, this is 

 shown to be unfounded, since albumin gives similar results, yet 

 contains no phosphorous, and is not chemically allied to nuclein. 



Probably the most important reason which led Fischer to under- 

 take this series of experiments was the claim that certain granules 

 of the Cyanophyceae should be identified as chromatin because they 

 behaved like chromatin when stained with haematoxylin. Fischer's 

 experiments not only overthrew this claim but raised the question 

 whether staining reactions ever indicate chemical composition. At 

 present, it would seem that, in most cases, the staining indicates only 

 physical differences. However, in some cases there is a chemical 

 reaction, e.g., when material fixed in bichloride of mercury is stained 

 in carmine, mercuric carminate is formed. 



It would be very convenient if we knew just how much depend- 

 ence should be placed upon staining reactions as a means of analysis. 

 If two structures stain alike with Delafield's haematoxylin, does this 

 mean that they have the same chemical composition; or if, on the 

 other hand, they stain differently, must they necessarily be different 

 in their chemical composition? Delafield's haematoxylin, when 



