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METHODS IN PLANT HISTOLOGY 
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 gentian-violet and 
the smaller the safranin. 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 proved that chromatin cannot be identified 
in this way 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. How¬ 
ever, 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 
carefully used, gives a rich purple color, but a careful examination 
will often show that in the same preparation some structures stain 
purple, while others stain red. Does this mean that the purple and 
red structures must have a different chemical composition ? Many 
people believe that structures which stain differently with a given 
stain must be chemically different, but they readily agree that struc¬ 
tures which stain alike are not necessarily similar in chemical com¬ 
position. Chromosomes of dividing nuclei and lignified cell walls 
