Boodle. — Anatomy of the Schizaeaceae. 395 
manes Prieurii the cavity-parenchyma becomes lignified, 
and one element of this tissue was noticed, which was much 
elongated, fibrous, and pitted like other fibres in the bundle, 
but with one or two protrusions on the side on which it was 
in contact with an annular tracheide. 
Sieve-tubes. 
In examining the sieve-tubes of the Schizaeaceae aniline 
blue and corallin-soda were at first used for the purpose of 
determining whether callus was present. These stains were 
however discarded 1 in favour of azo-blue, which was found to 
be preferable for several reasons. It may be stated at once that 
no callus was found in any of the Schizaeaceae examined, 
but, as it was found by experimenting with other plants, 
that azo-blue is an excellent stain for differentiating callus, 
it will be as well to describe the method of using it. Poirault 
(’ 93 , p. 139) recommends the use of azo-violet as a specially 
good stain for callus. Its action appears to be similar to that 
of azo-blue, for Mangin (’ 90 , p. 120) classes the two together 
with other dyes, and states that they are generally precipi- 
tated by acids, but stain cellulose and callus in a neutral or 
slightly alkaline solution. 
To prepare the stain, a little of the solid (Griibler’s azo- 
blue) is stirred up in water. It is practically insoluble, but in 
suspension has somewhat the appearance of a violet solution. 
A little caustic-soda or potash-solution is added until the 
colour becomes reddish, the solution is then shaken up and 
filtered, and a fairly dark red solution is obtained, which is 
the reagent for staining callus. This solution when exposed 
to the air gradually loses its alkalinity owing to carbonation 
of the potash, and finally turns violet, the stain being then 
precipitated. One can judge of the relative alkalinity of the 
red solution by the length of time a little of it in a watch- 
glass requires before assuming a violet tinge at the periphery. 
The dye gives the best results in a fairly strong but only 
1 Staining deep enough to colour very small masses of callus was found to incur 
a danger of staining proteid granules as well. 
