ASCOMYCETES 



21 1 



Host Plants. The following is a list of the natural hosts, as 

 compiled by Clinton: Ginseng, Aralia quinquefolia ; Begonia 

 rubra; Begonia sp. ; horse radish, Cochlearia Armoracia ; Cycla- 

 men sp. ; lupines, Lupinus albus, Lupinus angustifolius, Lnpinus 

 lutens, and Lupinus thermis ; Nemophila auriculata ; tobacco, 

 Nicotiana Tabacum ; Onobrychis Cristagalli ; pea, Pisum sa- 

 tivum ; Trigonella ccerulea ; and violet, Viola odorata. It is 

 therefore evident that a variety of dicotyledonous plants may 



Fig. 82. The Thielavia Disease of Tobacco. (After G. P. Clinton) 

 Healthy and diseased root systems 



be attacked. The leguminous hosts are, however, most numerous, 

 and the fungus is quite frequent on garden and sweet peas. 



Pathological effects. Roots affected by the Thielavia do not 

 develop a normal root system, or they may be injured to such 

 an extent that on pulling up an affected plant from a moist soil 

 practically everything except a stub of a root will be broken off. 

 In the case of the tobacco a cluster of new roots may form on 

 the crown above the first injuries (Fig. 82). The fungus is ap- 

 parently most injurious in the seed beds. Affected plants may 

 not be killed, and many go through the season with a stunted 

 growth, or with such a check upon vigorous development at the 



