GENERAL REMARKS ON STAINING 77 



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 differen- 

 tiating structures, and in bringing out details which would otherwise 

 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 experienced tech- 

 nician 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, hke Haidenhain's iron- 

 alum haematoxylin and Flemming's safranin, gentian violet, orange, 

 require patient study and long practice before they yield the magnifi- 

 cent preparations of the trained cytologist. The beginner, especially if 

 somewhat unacquainted with the details of plant structure, may be- 

 lieve 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 vio- 

 let. 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 are quite different and starch grains are well 

 differentiated in the tube cells and the wall shows a violet intine con- 

 trasting sharply with a red exine, the mount is good. Anything inter- 

 mediate is indifferent. If mitotic figures have been stained with cyanin 

 and erythrosin, a first-class preparation should show blue chromo- 

 somes and red spindles; if stained with safranin and gentian violet, the 

 chromosomes should be red and the spindles, violet. 



In staining growing points, apical cells, young embryos, antheridia, 

 archegonia, and many such things, the cell walls are the principal 

 things to be differentiated, if the preparations are for morphological 

 study. As a rule, it is better in such cases not to use double staining, 

 but to select a stain which stains the cell walls deeply without obscur- 

 ing them by staining starch, chlorophyll, and other cell contents. For 

 example, try the growing point of Equisetum. The protoplasm of such 

 growing points is very dense. If Delafield's haematoxyhn and eryth- 

 rosin be used, the haematoxyhn will stain the walls and nuclei, and 



