400 BOTANICAL GAZETTE [MAY 
Albumen fixative is much improved if, instead of water, the bichro- 
mate solution is used. 
In the foregoing process the strength of the bichromate solution 
seems to be immaterial. If it is stronger than 1 per cent, crystals 
will appear when the preparation dries. These crystals do no harm, 
since they never appear in the sections, but they leave unsightly 
spots on the glass. In practice a 0.2 per cent bichromate solution 
will be entirely satisfactory. The writer does not make a solution 
of definite proportions, but adds enough potassium bichromate crys- 
tals to make the water pale yellow. A very small quantity of a 
salt of chromium is sufficient, in the presence of light, to render 
gum and gelatin insoluble in water. 
Imbedding in gelatin 
In preparing hard woods for sectioning it is the custom to soften 
in hydrofluoric acid and imbed in celloidin. Since this process 
involves dehydration, some refractory woods become unmanageable 
when sectioning is attempted. 
In connection with the work of M. A. BRANNON on the extremely 
hard stems of plants which had been submerged by the rising waters 
of the Salton Sea and then exposed when the water receded, a 
method of imbedding in gelatin was devised by the writer and suc- 
cessfully used. Many of these stems were decorticated, some part- 
tially macerated, and all were excessively hard. 
Gelatin is soaked in water until no more is taken up, the excess 
water drained off, and the gelatin liquefied by heat. Pieces of 
wood previously softened in water, or if necessary in hydrofluoric 
acid, are placed in the melted gelatin for some hours: Small blocks 
of hard wood to serve as supports in the microtome are also placed 
in the melted gelatin. The blocks tobe sectioned are properly 
oriented in a gelatin matrix on the supporting blocks, cooled to set 
the gelatin, and plunged into strong formalin to harden the gelatin. 
In cutting the knife is flooded with water. 
The advantages of this method are that no dehydration is neces- 
sary; that the process is very rapid; and that partly disintegrated 
tissues are held in place. In careful hands sections of hard w 
can be cut as thin as is possible by the celloidin process. 
