with special Reference to the Mode of Connexion of Cells. 103 



that of tlie ordinary vegetative tissue of Pliaseolus vulgaris, Tamus 

 communis, Nerium oleander, Salisburia adiantifolia, &c, small pieces 

 are killed and swollen in an aqueous solution of picric acid, and then. 

 fixed in the Kolossow's reagent and preserved in thymol water. 

 Finally, where the tissues are more resistant, as, for instance, in 

 li'jhinia pseudacacia, Prunus laurocerasits, or Aucuba japonica, treat- 

 ment with picric acid may be followed by more severe swelling by 

 means of solutions of zinc chloride or sulphuric acid, to be succeeded 

 as before by fixing, hardening, and preserving. The blackening of 

 the cell contents caused by osmic acid may be removed by bleaching. 



From such preserved material sections may be cut when required. 



The process of staining is no less complicated than that of killing 

 and fixing, and is best considered under two heads, viz. : — (1) The 

 methods applicable to certain endosperms and tissues of similar 

 character. (2) The methods applicable to the majority of tissues. 



In certain special cases it is possible to stain the threads directly 

 either with safranin alone or by introducing safranin by means of a 

 somewhat intricate substitution method such as that which I used 

 with excellent results in the case of the endosperm of Tamus com- 

 munis, where the sequence of staining was Hofmanms blue (or 

 so;uble water blue), methylene blue, safranin, and in which more- 

 over the Hofmann's blue was dissolved in dilute picric acid or 

 uranium nitrate, and the methylene blue in dilute salt solution. 

 Once stained with safranin, all sorts of modifications are possible. 

 Thus, the safranin may be succeeded by gentian violet or by eosin, and 

 with gentian violet Gram's method is applicable and most advan- 

 tageous. As safranin forms a precipitate with chromic acid, sections 

 siained with safranin may be treated with this reagent, and then 

 with silver nitrate, thus effecting a silver staining of the threads. 

 Silver nitrate itself also forms a precipitate with safranin. k a.i 

 cases the staining is practically limited to the threads. 



When the above methods of direct selective staining are appliel 

 to ordinary tissue they are found to fail, for it usually happens that 

 the whole of the wall becomes deeply stained, so that the threads 

 are no longer visible. I was for some time completely baffled by this 

 circumstance, but I ultimately adopted the well-knowm method of 

 staining and washing out, using for the purpose orange Gr or acid 

 f uchsiu. With ordinary tissue the staining appears to be more easily 

 "accomplished than with the thick mucilaginous walls of endosperm 

 cells, and the method may be somewhat more syncopated. Excellent 

 results may be obtained by staining at once with safranin and wash- 

 ing out with orange Gr. This may be followed by staining with 

 gentian violet, succeeded by treatment with acid fuchsin, or the 

 sequence of staining may be safranin, gentian violet, acid fuchsin. 

 Substitutions in which safranin, gentian violet, a nd eosin are included 



