1904 | BRIEFER ARTICLES 457 
tion added to it to keep it of a deep brown color. Moderate heat — 
o° C.-—hastens the process. Chromic acid and chromates, though 
extremely useful fixing agents for certain kinds of objects, are not atall 
desirable for lignified tissues, as they are rendered yet harder by the 
use of these reagents. 
Il. Desilicification, etc—Woody tissues usually contain more or 
less silica and other mineral deposits which render sectioning difficult 
or impossible. Hence it is of primary importance that these substances 
be removed as thoroughly as possible. For this purpose dilute hydro- 
fluoric acid is indispensable. A 10 per cent. aqueous solution of the 
commercial acid is most useful. This may be kept ina bottle coated 
internally with a thick layer of hard paraffin. The blocks of material 
are transferred directly from the water in which they’were boiled, or 
from the 80 per cent. alcohol and iodin, as the case may be, and are 
kept in the acid three or four days, with one or two changes of the 
acid and frequent shaking of the bottle. Wash out the acid thoroughly 
in running water for two to four hours. This treatment frees the 
tissues completely of all mineral deposits, while the organic structure 
remains unaffected. It has been shown’ that cellulose, constituting the © 
cell-walls of plants, when freed from mineral deposits is of practically 
uniform hardness, regardless. of the plant or part of the plant in which 
it may occur. This hardness is about equal to that of muscovite, while 
the tissues in their natural condition often are equal in hardness to 
calcite, fluorite, or even opal. ence it is evident that the usefulness 
of hydrofluoric acid in this connection can scarcely be overestimated. 
Ill. Dehydration The water must be again removed from the 
material by passing it through alcohols of grades 30, 50, 70, go per 
cent., and absolute, allowing twelve hours in each grade. At least one 
change of absolute alcohol is usually desirable, as complete dehydra- 
tion is of the first importance. The remaining air should be removed 
from the blocks when they are in 60 or 70 percent. alcohol, by means 
of the vacuum pump. 
IV. Jnfiltration with celloidin— Make a series of celloidin solutions 
by dissolving Schering’s celloidin (Schering & Glatz, New York) in 
equal parts of ether and synthol or absolute alcohol. There should be 
ten grades: 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 per cent. For the 2. 
per cent. solution take two grams of celloidin to 100” of the ether and 
synthol, or ether and absolute alcohol mixture. For 4 per cent. take 
Ort, EmMa, Beitrage zur Kenntniss der Harte vegetabilischer Zellmembranen. 
Oesterr. Bot. Zeitschr. 50: 237-241. 1900. 
