May, 1905.] 
Imbedding Plant Tissues. 
345 
block, let it cool for a few seconds and place one of the pieces of 
material on the block and cover with more agar-agar. Allow it 
to cool for a few minutes, when it is removed from the block and 
placed in 70 per cent alcohol and passed thro the different grades 
of alcohol to paraffin and imbedded. The tissues should remain 
for two or more hours in each of the different grades of alcohol. 
No albumen fixative is necessary to attach the sections to 
the slides and the sections can be stained as any other paraffin 
sections. Delafield’s haemotoxylin and Safranin and gentian 
violet are favorable stains. The agar-agar surrounding the sec- 
tions stains in Delafield’s haemotoxylin but it takes only a slight 
stain in Safranin and gentian violet. 
It seems that this method will be verv valuable for section- 
ing tissues that would be easily torn by the ordinary paraffin 
method, and especially applicable in the study of rusts and other 
parasitic fungi. The layer of agar-agar around the tissues 
becomes very tough when passed thro the alcohols and forms a 
firm medium which prevents the tissue from being torn when 
sectioned. 
The Phyllachora mentioned above, was dried and kept in 
the herbarium. The material was firmly pressed and thoroughly 
dry and in spite of these facts, the perithecia were sectioned 
without any injury and the hyphae could be seen in the adjacent 
tissues of the leaf. The Uromyces was collected in October, 
1904, and the tissues of the leaf were entirely dead. The sec- 
tions showed the delicate teleutosorus and spores in fine condi- 
tion. The parts sectioned were cut into small pieces and placed 
in hot water at about 70° C. for an hour and then transfered to 
a 10 per cent solution of hydro-fluoric acid for twelve hours to 
remove the silicon which would otherwise interfere with the 
sectioning. The material was washed and imbedded in the 
manner already described. The stem of Equisetum was also 
herbarium material and was treated in the same manner as the 
Phyllachora and Uromyces. The sections obtained were in good 
condition for such material. The beech leaf was from alcoholic 
material and the sections showed the different parts of the leaf 
in excellent form. This method can be used to the best advan- 
tage where a histological study of the plant tissue is desired. 
It is much shorter than the oridnary paraffin method as the 
aqueous solutions of agar-agar penetrate the tissues withotxt any 
preliminary dehydration. Serial sections were cut as thin as lOa. 
A few scale insects found on a palm were also imbedded and 
sectioned and fairly good sections were obtained. This method 
will perhaps be useful in the study of insects. 
