GENERAL REMARKS ON STAINING 
73 
stain alike with safranin; chromosomes and cellulose cell walls stain 
much alike with Delafield’s haematoxylin; but everyone recognizes 
that the chromosome is very different in its chemical composition 
from either the cellulose or the lignified wall. 
However, in an indirect and somewhat uncertain way, one can 
infer the nature of certain structures from the staining. For instance, 
if sections of various objects have been stained with safranin, we may 
draw the following inferences with more or less confidence: if cells 
in the xylem region of a vascular bundle stain red, their walls are 
lignified; if cortical cells, which may appear quite similar in transverse 
section, stain red, they are likely to be suberized; if the outer walls 
of epidermal cells stain red, they are cutinized; but if the outer 
boundary of the embryo sac of a gymnosperm stains red, it is chitin- 
ized. Of course, these inferences can be made only because the 
various structures have been tested by more accurate methods. 
Whatever doubt or uncertainty there may be in regard to theories 
of staining or in regard to the value of stains as a means of analysis, 
there is no doubt that stains are of the highest importance in differ¬ 
entiating structures, and in bringing out details which would other¬ 
wise be invisible. 
PRACTICAL HINTS ON STAINING 
The number of stains in the catalogues is becoming so great that 
it is impossible to become proficient in the use of all of them. As 
we have already intimated, it is better to master a few of the most 
valuable stains than to do indifferent work with many. An experi¬ 
enced technician knows that it is impossible to judge from a few 
trials whether a given stain or combination is really valuable or 
not. As a matter of fact, some of the most valuable combinations, 
like Haidenhain’s iron-alum haematoxylin and Flemming’s safranin, 
gentian-violet, orange, require patient study and long practice before 
they yield the magnificent preparations of the trained cytologist. 
The beginner, especially if somewhat unacquainted with the details 
of plant structure, may believe that he has an excellent preparation 
when it is really a bad, or at most an indifferent, one. To illustrate, 
let us suppose that sections of the pollen grain of a lily have been 
stained in safranin and gentian-violet. If the preparation merely 
shows a couple of dense nuclei and a mass of uniform cell contents 
surrounded by a heavy wall, the mount is poor. If the two nuclei 
