in Blechnum and Osmund a. 31 
escape of the mucilage contained in them. Chromic acid is 
more satisfactory. A solution of 1*5 to 2*o per cent, strength 
was employed and the tissue was exposed to its action for 
twenty-four hours and was then freely washed in water. By the 
use of so strong a solution the voluminous tannin-precipitate 
which first appears is subsequently dissolved in the excess of 
the reagent, and after washing the cell appears clear and the 
tannin has been removed 1 . The observation of fresh material 
mounted in iodine or in *5 to 1 per cent, of osmic acid gives 
excellent results 2 . With iodine the deeply stained brown 
protoplasm and nucleus are sharply contrasted with the clear 
yellow mucilage, and with osmic acid the mucilage-drops 
which contain tannin stand out dark and well defined, while 
the ectoplasm and the endoplasmic framework remain hyaline 
and brilliant with just the faintest yellow coloration. With 
both these reagents the cell-contents are exceedingly well 
preserved. 
Picronigrocin (24 hours) was also employed with success, 
and such material, after washing in water and mounting in 
glycerine, furnished quite the most satisfactory permanent 
preparations. As staining reagents, iodine, osmic acid, 
Hanstein’s violet-fuchsin, haematoxylin, methylene-blue, Hof- 
mann’s blue, and eosin were chiefly used. Both Hanstein’s 
violet-fuchsin and eosin were especially valuable, not only on 
account of their staining properties, but also for the comparative 
rapidity with which they diffused into the cell contents ; with 
these exceptions, the aniline dyes penetrated the mucilage 
with great difficulty, and long and patient treatment, with 
repeated observation, was required. In the various details of 
washing, and during micro-chemical investigation, the well- 
known refractory properties of mucilage were only too well 
marked, rendering much of the necessary manipulation both 
trying and tedious. 
1 This method was first used for the tentacles of Drosera. See Gardiner in 
Proc. Roy. Soc. 240 (1886). 
2 This applies to Blechnum only. The hairs of Osmunda contain such an 
enormous quantity of tannin that the whole of the tincture is blackened. 
