396 Boodle. — Anatomy of the Schizaeaceae. 
slightly alkaline solution. When testing for callus it is 
advisable always to work with a section of Cucurbita used 
as a control, to be stained in the same watch-glass with the 
other sections. This shows at once whether the dye is working 
properly. If the staining solution is strongly alkaline, it will 
stain all parts of the section, but if rightly used it produces 
remarkable differentiation, when any callus is present. Sec- 
tions may be left for ten minutes or more in the stain, 
according to its strength. They are then transferred to a 
slide, the stain is drained off, and a few drops of water are 
added until the sections change from red to lilac or bluish 
or nearly colourless, as the case may be. They are then 
examined at once, and the callus if present is found to be 
crimson, while cellulose walls are generally lilac or blue, 
but proteid and also lignified walls are entirely uncoloured. 
In time the callus turns violet and its colour finally fades, 
but when first mounted as above, the callus is the only red- 
stained substance in the section, and is deeply stained. The 
staining should be done in a watch-glass, which is covered up, 
so that the solution may not turn violet throughout during 
the operation. 
The following were the examples tested with azo-blue in 
the Schizaeaceae : — 
Lygodium japonicum , petiole ; L . dichotomnm , petiole ; 
Schizaea digit at a ^ rhizome; Anemia Phyllitidis , petiole; 
Mohria cajfrorum , petiole. No callus was found in any of 
the specimens examined. A similar negative result was 
obtained in the Hymenophyllaceae. In this family the sieve- 
tubes were tested with azo-blue in : — Trichomanes radicans y 
rhizome and petiole ; Trichomanes Prieurii^ petiole ; Hymeno - 
phyllum demissum , var. nitens , rhizome. 
The results obtained with azo-blue in other Ferns may as 
well be mentioned. Well-marked callus occurs on the sieve- 
plates of the end-walls and vertical walls of the sieve-tubes in 
both rhizome and petiole of Pteris aquilina. Equally distinct 
callus was also found in the petiole of Thyrsopteris elegans , 
and in the rachis of Onoclea germanica. A small amount was 
