259-J Journal of Applied Microscopy 



For fixing and embedding only a small amount of the agar-agar solution need 

 to be taken. The solution should be kept at a temperature of 70° C. The fresh 

 tissues are first placed directly into the hot "2 per cent, solution and let remain 

 for about two hours and are then transferred to the 5 per cent, solution and let 

 remain for one hour or more, when they are ready to be embedded. The tissues 

 are embedded on wooden blocks. With a small camel's hair brush put a layer of 

 the hot agar-agar on one end of the block, let it cool for a few seconds and then 

 place one of the pieces of material on the block. Cover with more of the agar- 

 agar solution until properly embedded. After fixing the tissue to the block, place 

 in !I5 per cent, alcohol and let remain for twelve hours. The longer the agar-agar 

 remains in the alcohol the tougher it becomes. The writer left embedded mate- 

 rial in alcohol for six weeks without any noticeable injury. The material is 

 sectioned on a sliding microtome the same as in celloidin sections. The knife 

 must be very sharp, as the sections are somewhat friable, and kept moist with 95 

 per cent, alcohol, and likewise the blocks, during the sectioning. The sections 

 can be stained the same way as celloidin sections. Safranin and gentian violet, 

 and Delafield's hematoxylin are favorable stains. 



It seems that this method will be especially valuable in the study of rusts 

 and other parasitic fungi where it is advantageous to make microscopic sections. 

 The Phyllostictia, mentioned above, was collected in October and was the late 

 infection. The tissues of the leaf were entirely dead. The infected parts were 

 cut in small pieces and placed directly in the hot 2 per cent, solution of agar- 

 agar for two hours, and in the 5 per cent, solution for an hour, and then embed- 

 ded. The sections obtained were cut at 20/v and showed the conidia and spores 

 in fine condition. The rust on the raspberry was collected in September, 1902, 

 dried and kept in the herbarium. The material was very firmly pressed, 

 thoroughly dry and brittle, but in spite of these facts the sections were as satis- 

 factory as in the fresh material. The delicate peridium was sectioned without 

 any injury and the hyphai could be seen in the adjacent tissues of the leaf. The 

 parts sectioned were placed in warm water about 70° C. and let remain for two 

 hours, then in the hot 2 per cent, agar-agar solution for two hours and then in 

 the 5 per cent, solution for an hour and embedded. The sections were cut at 

 20//. The sections containing the fungi were taken through the alcohols to 

 water and stained in a weak solution of safranin, then washed and mounted in 

 glycerine. 



This method is applicable where a histological study of the plant tissue is 

 desired, but does not seem satisfactory for cytological work. Sections were cut 

 at 20// in thickness, but the most were cut at 25yu and 30//. The best feature of 

 this method is that it is simple and quick. The aqueous solution of agar-agar 

 at once penetrates the tissues without any preliminary dehydration. 



Botanical Laboratory, Ohio State University. HarLAN H. YoRK. 



