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 i 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 o. 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 par- 

 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 to be 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 woods 

 can be cut as thin as is possible by the celloidin process. 



