332 THE MICROSCOPICAL NEWS. 
When there is no disengagement of red vapour at the normal 
temperature, set fire to the alcohol in order to concentrate it 
further, and warm the watch-glass on a piece of wire-gauze over a 
gas-burner or spirit lamp. 
Under these conditions the cell-walls undergo a considerable 
thinning, but all their contents disappear. They become so 
delicate that the difficulty is to remove them from the water in the 
evaporating dish (into which the watch-glass has been emptied) 
to transfer them into the glycerin of the slide. We attain this 
object by adding to the still warm alcohol a little chloroform ; this 
treatment hardens the preparations, which can then be transferred 
by means of little wooden spatula into the glycerin, where they soon 
recover the same flexibility as in the watch-glass. 
We have obtained better photographs of vegetable sections thus 
prepared than with those obtained by other processes. 
Chromic acid.—According to Hohnel this acid gives trans- 
parency to tissues of a corky nature, such as cells of cork, epider- 
mis, cuticles, and the envelopes of pollen-grains, to the extent of 
making details perfectly visible, which, without the aid of reagents, 
could not have been seen. 
The solution of chromic acid admits of very different degrees of 
concentration, the important point being that it should be free 
from sulphuric acid. 
Calaum chloride.—When it is desired to give transparency to 
the preparation without thinning it, it may be very useful, espe- 
cially if the tissues are young, to have recourse to the process 
employed by Treub,{ and afterwards by Flahaut,§ which consists, 
as described by the latter author, “in placing the sections in a 
watch-glass or in a small porcelain capsule with one or two drops 
of water ; the drop is covered with a little dry calcium chloride in 
powder, and slowly warmed over asmall flame until the desiccation 
is nearly complete. The sections are withdrawn directly from the 
action of the flame, and a few drops of water added, which dissolve 
the calcium chloride. The sections immediately float in the 
water ; they need only be collected and placed in the glycerin, in 
which they attain sufficient transparency after a few hours. This 
treatment results, not in dissolving all that the cells contain, but in 
darkening their contents by slightly thickening the originally very 
thin walls ; these walls become at the same time clear and brilliant. 
The opacity of the cell-contents obstructs the study of several layers 
of cells at the same time. * 
+ “ Ueber Kork,” SB. Wiener Akad., 1877, 1 Abth. 
+ ‘Le méristeme primitif de la racine des monocotylédones.’ Leyde, 1876. 
§ << Recherches sur l’accroissement terminal de la racine chez les Phanéro- 
games,’ Ann, Sci. Nat., vi. (1878) p. 24. 
