1920] CURRENT LITERATURE 189 



gradations in dependence upon the mycorhizal habit. Some will make only 

 a very slight mycelial growth in cultures, while others will form abundant 

 mycelia, but never develop carpophores. Field experiments also confirm this 

 mycorhizal dependence, but attempts to trace mycelium from carpophore to 

 tree were seldom successful. He considers the mycorhizal relationship to be 

 symbiotic, the green plant furnishing carbohydrates and in return receiving 

 water and salts, especially nitrogenous substances which the fungi probably 

 obtain by the fixation of free nitrogen. 



As a source of cultures he first tried the germination of spores. Various 

 media and methods of treating spores were tried, but no germinations from 

 mycorhizal forms such as tubers or amanitas were obtained, and from other 

 forms the mycelium obtained was seldom vigorous. Because of this he resorted 

 to the use of portions of the carpophore, flamed over a Bunsen burner, as a 

 source of cultures, and found this (which he erroneously considers a new 

 process) much more satisfactory. In this manner he obtained cultures of 24 

 species which he describes, giving figures for 17 of them. While many media 

 were used, he found a decoction from carrots, solidified with gelose (a gum 

 derived from agar-agar), the most satisfactory. Cultural variations bring into 

 question the validity of some specific characters, such as size, color, and 

 characters due to substratum. 



In his studies of Morchella cultures were obtained from single spores. The 

 mycelium was very vigorous, growing well at 10-12 C. Sclerotia 0.5-4 mm. 

 in diameter appear in 10-15 days. No conidia or ascocarps were formed. 

 He attributes the absence of ascocarps either to the limited mycelial growth in 

 cultures, or, as he considers more probable, to the necessity of a mycorhizal 

 host prior to ascocarp formation. 



Cultures obtained from the spores of Psaliota were always weak, while 

 those from portions of the carpophore were very vigorous. From his pure 

 cultures he easily developed successful commercial spawn. Cultures from one 

 carpophore always developed carpophores with the same varietal characters 

 as the original, which is a great practical advantage.— Leva B. Walker. 



Identification of mahoganies. — To meet the need of some adequate method 

 for distinguishing the different commercial timbers now classed as mahoganies, 

 Dixon 20 has prepared (1) a concise working definition of the term mahogany, 

 and (2) an anatomical key accompanied by detailed descriptions for the 

 identification of some of the more common kinds by means of their microscopic 

 characters. The constant increase in the number of species of mahogany- 

 yielding trees in economic use, and the doubtful authenticity of many of the 

 specimens derived from commercial sources, have made the construction of 

 such a scheme of classification most difficult. 



*° Dixon, H. H., Mahogany, the recognition of some of the different kinds by 

 their microscopic characteristics. Notes from the Bot. School, Trinity College, 

 Dublin 3:58. pis. 22-54. 1919. 



