no Oliver. — On the Obliteration of 
It is prepared by adding rosolic acid to a strong aqueous 
solution of sodium carbonate. The dye so obtained stains the 
callus with great avidity a brilliant rose-pink. Unfortunately 
the stain is not a permanent one, as preparations mounted in 
glycerin gradually fade, and in about four days’ time are 
almost colourless. It is further necessary to use this reagent 
freshly made up. For forty-eight hours after making it will 
stain well enough, but after this period this capacity is 
gradually lost. With the callus-plates in question I obtained 
most satisfactory results ; they stained indeed as satisfactorily 
as those of Cucurbita could. 
(3) Bismarck-brown dissolved in water is also a reagent 
which stains callus. It is not so satisfactory as the above, or 
as Hoffmann’s blue, since the whole section is stained by it, 
though it should be pointed out that the different layers of the 
cell-wall are very beautifully differentiated. In the callus- 
plates of the sieve-tubes proper of Macrocystis I was able, 
with this reagent, to make out a very decided stratification. 
This reagent acts best when recently made up. 
(4) Hoffmann s blue. — This is probably the soluble aniline 
blue used by Russow 1 , and considered by him to be an 
eminently characteristic callus-reagent. I always used it 
dissolved in 5o°/ 0 of alcohol, and obtained the best results with 
the callus-plates in question. Sections should remain in it 
twenty-four hours, and be then washed in water and mounted 
in glycerin. Under these conditions the colour is not retained 
in the cell-walls, but the callus-plates remain a very brilliant 
blue, which is permanent. I have preparations which have 
been made for three months, and exposed to the light all the 
time, and so far have not at all faded. 
(5) Chlor zinc-iodine does not, as a rule, stain the callus- 
plates in Macrocystis or Nereocystis ; they swell up under its 
action and show stratification. In a young specimen of 
Nereocystis Liitkeana is a trumpet-hypha about the same 
1 Russow, Callusplatten bei den Gefasspflanzen, in Sitzb- d. Dorpat. Nat. Ges. 
1881, p. 63. 
