[Vol. 2 



414 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



familiar with it in the different stages of development it is 

 at all times an organism with striking characteristics. Such 

 differences in appearance as may be found in comparable 

 stages on the various hosts may be regarded as causally re- 

 lated to the host substratum, or, at least they may be so re- 

 garded until adequate morphological differences or contrast- 

 ing physiological relations are estab- 



appearance of 



lished. The 



general 



affected roots of asparagus, carrot, 

 beet, or alfalfa are well expressed in 

 some of the common names applied, 

 such as red root, root felt disease, 

 violet fungus, etc. 



With sufficient time for abundant 

 growth the fungus completely in- 

 vests the root or root system with a 

 mantle, weft, or mat of hyphae of 

 characteristic color. In the early 

 stages of growth on the root the 

 mycelium is pale buff to violaceous, 

 but when the root is completely in- 

 Fig. 1. Rhizoctonia, Cro- vested, the mycelium is red-violet to 



h Jl violet-brown, and always violet- 



brown with age or when densely matted. The numerous small 

 darker papillae or " minute sclerotia" in the mantle of 



mycelium are in reality cushion-like mycelial bodies described 

 later. 



In the following description the writer will not attempt to 

 follow all changes in the development of the various mycelial 

 conditions, but will endeavor to give briefly those develop- 

 mental features 



characteristics which may be applied to most herbarium ma- 

 terial. For further morphological details the accounts of L. 

 and C. Tulasne ('62) and Prillieux ('91) should be consulted. 



The external, general hyphae are more or less different in 

 form and appearance with age. The younger hyphae are 

 usually dilutely violaceous with a pigment which may be 

 decolorized by the application of acidulated water. The pro- 



of greatest interest 



and those diagnostic 



