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 very 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 without any 

 preliminary dehydration. Serial sections were cut as thin as 10//. 



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. 



