452 FUNGOUS DISEASES OF PLANTS 



upon the majority of hosts the Corticium stage disappears by the 

 time the host plant is dead. 



A considerable amount of study is demanded in order that it may 

 be determined what may properly be considered species or varieties 

 within this group of plants. Cross-inoculation work is particularly 

 important, yet it is also difficult, on account of the following fact : 

 After being grown in culture for some time the fungus seems to 

 change to a certain degree, at least, its relation to the host as a 

 parasite, and it is possible that direct transference of the fungus 

 from one host to another would not yield the same results as by 

 the use of old cultures or cultures grown upon diverse media. 



This fungus in all of its forms is readily culturable upon the 

 ordinary nutrient media, such as bean stems, potato and beet cylin- 

 ders, agars, corn meal, etc. It is, moreover, not difficult to make 

 dilution cultures, even though the fungus usually grows upon those 

 parts of the plant where bacteria would normally be present in 

 abundance, as upon roots and underground stems. By carefully 

 washing the mycelium in distilled water and then by the use of 

 acidulated media, as suggested under cultural methods, the fungus 

 may be readily separated from contaminating bacteria. 



Control. No effective preventive measures for the forms of this 

 fungus have yet been found. It would appear, however, that gen- 

 eral sanitary precautions are important. Good drainage in the 

 upper layer of the soil and the presence of a layer of sand, charcoal, 

 or cinders serve in great measure to prevent the appearance of 

 the fungus. An aerated soil is also less liable to be seriously 

 affected, owing, perhaps, to the better health of the roots than one 

 which is poorly aerated. The application of lime and other fungi- 

 cidal mixtures to a soil is commonly useless. This fungus is 

 apparently not readily affected either by weak alkalis or acids ; but 

 since acid conditions render the host more susceptible, liming has 

 value. 



V. HEART ROT OF SUGAR MAPLE 



Hydnum septentrionale Fr. 

 ATKINSON, GEO. F. Geological Survey of La. (1889): 335-336. pi. 38. 



Among the numerous species of the genus Hydnum, which 

 embrace the commoner toothed Basidiomycetes, it would seem 



