1914] 



BURT THELEPHORACEiE OF NORTH AMERICA. I 195 



The microscopical technique has been simplified as much as 

 possible. Usually dried herbarium material had to be used for 

 study and proved very satisfactory except in the case of speci- 

 mens which had been subjected to poisoning processes for pres- 

 ervation in herbaria. A small bit of the fructification having 

 a promising hymenial surface 2 or 3mm. square but smaller if 

 the specimen is a valuable type is first moistened with alcohol, 

 then wet with water and cut out from the rest of the specimen 

 and from the substratum. This bit is then placed in a holder 

 of elder pith and oriented so that the sections may be cut per- 

 pendicular to the surface of the hymenium and also contain as 

 long hyphse as possible. The sections are cut as thin as possible, 

 free hand, with a very keen section razor flooded with alcohol. 

 The thinnest sections are placed on a slide in a drop of water 

 and then a drop of seven per cent aqueous solution of potassium 

 hydrate is added. 



Close observation of the sections should be made when the 

 potassium hydrate solution comes in contact with them. For 

 most species, the sections are merely cleared and the hyphse 

 swelled to the normal size of vegetative hyphse. In a few species, 

 the alkaline solution may dissolve out the color of the section 

 on coming in contact with it, or it may change this color to a 

 violet, which finally disappears, or it may cause disorganization 

 changes in certain structures leading to their disappearance or 

 destruction. Such changes should be observed and noted, for 

 they are of help in the determination of the species. In the 

 cases in which potassium hydrate solution exerts a destructive 

 action, lactic acid should be employed with other sections in 

 the manner described for potassium hydrate. Lactic acid 

 clears and swells sections well, but so much more slowly than 

 potassium hydrate that I have used it only where the latter is 

 not satisfactory. After the sections have been cleared, the 

 potassium hydrate should be drained off, the sections lightly 

 stained on the slide with alcoholic solution of eosin (but not 

 overstained), mounted in water, and studied at once. 



For a thorough study of the species of the family at least one 

 permanent preparation of each species should be retained for 

 future comparisons. Permanent preparations may be made 

 from the temporary water mounts by adding dilute glycerin 



