290 BULLETIN No. 189 [June, 



The presence of the Corticium stage seems to depend on climatic 

 conditions. A cool season with an abundance of moisture is appar- 

 ently essential for its development in the field. This stage is gener- 

 ally found on plant tissues that are perfectly healthy ; it is in no way 

 injurious to them. Some cases have been found where it had devel- 

 oped on stems almost cut off by Rhizoctonia, but in no instance has 

 the writer seen it form directly on a lesion or on injured tissue. (Sec 

 Figs. 6 and 7.) 



The development of the Corticium stage may be described as fol- 

 lows : The dark brown hyphae of the sterile stage gather, usually at the 

 base of the plant, and from them arises an ashy gray mycelium, which 

 forms a fine network around the stem. The development is usually 

 faster where a little soil, thrown up by the rains, has formed a film 

 around the stem. The extent of this fruiting layer varies, but it may 

 proceed several centimeters up the stem. It is so lightly attached to 

 the plant that it may easily be rubbed off. As it becomes old, it cracks 

 and falls off. 



The outer hyphae of the fruiting layer bear club-shaped basidia 

 with four sterigmata and spores. Cystidia are lacking. The spores 

 are colorless, oval to ovate, and have pointed bases. The usual spore 

 measurement varies from 9 to 14 /x by 6 to 8 p. 



Cultures of Rhizoctonia from single spores of the Corticium stage 

 have been obtained both by dilution methods and by the method used 

 by Rolfs, 94 which consists in placing a stem covered with the fruiting 

 stage over an open petri dish containing a nutrient agar, and allowing 

 the spores to drop on the agar. 



Another fungus belonging to the genus Corticium, C. oclira- 

 Icucum (Noack) Burt (see footnote b, page 287), found in the United 

 States by Stevens and Hall 117 ' 119 011 pomaceous fruits, has been care- 

 fully examined by the writer. The mycelium of this species corre- 

 sponds in many respects to that of R. Solani and the development of 

 the perfect stage is similar to the development of the Corticium stage 

 of that species. It appears that these two species are very closely re- 

 lated, but are entirely distinct forms. 



Duggar, a w r ho has had an opportunity to study R. Crocorum 

 (Pers.) DC. more at length, gives the following description of this 

 species in his recent work : 



"The external, general hyphae are more or less different in form and appear- 

 ance with age. The younger hyphae are usually dilutely violaceous with a pigment 

 which may be decolorized by the application of acidulated water. The protoplasm 

 is dense towards the tips of branches and vacuolated farther away. The hyphae 

 are somewhat flexuous, branched (sometimes closely), with the branches arising 

 at right angles to the main hypha, and with a partition wall laid down at not 

 over 10 p. distant. With age the hyphae become rigid, somewhat less in diameter, 

 4-8 fji, the branching is distant, and these branches readily break off at the first 

 partition wall. At the point of union the diameter is uniform with the main 



See footnote, page 284. 



