5 so SPECIAL PLANT PATHOLOGY 



pecially in low-lying country, as along stream banks, or in closed-in 

 valleys. Whole trees are practically attacked, the young leaves turn 

 brown and then they begin to wither and finally curl up into a brittle 

 mass. It also produces spots on the leaves of the white, black, and 

 scarlet oaks. 



Until the life history of this fungus was fully known, it was con- 

 sidered as three distinct types of imperfect fungi by the older my- 

 cologists. The fungus known as Glceosporium nervisequum represents 

 the stage, which appears upon the leaves in the form of pustules, or 

 acervuli, especially localized upon the veins of both the upper and 

 lower leaf surfaces. Ovate conidiospores measuring lo to 15/x X 4 to 6/x 

 are formed upon small colorless conidiophores. 



The acervuli measure 100 to 300/x in diameter and in moist weather 

 the numberless spores are ejected in creamy masses, or strings. The 

 same stage was known on the twigs by the generic name of Myxosporium. 

 The Sporonema stage is represented by the pycnidium, which develops 

 from the stroma of the fungus and the interior of the pycnidium is 

 lined by inwardly projecting conidiophores, which abstrict pycnospores. 

 The ascigeral stage is found on old leaves that have remained over 

 winter in the open, and it may appear in late winter or early in the 

 spring. The perithecia are not uniform in size, for we find them 

 measuring in diameter from 150 to 250/u with a beak 50 to loo/x long. 

 The broadly clavate asci are bent at right angles near the base. They 

 have a thickened apex, a terminal pore with a surrounding refractive 

 ring and bear invariably eight hyaline two-celled elliptic ascospores. 

 The two ascospore cells are unequal in size, the larger of the two giving 

 rise to a germ tube. 



Application of the 5-5-50 Bordeaux mixture to young shade trees 

 and to nursery stock assists in controlling the disease. 



Tobacco {Nicotiana tabacum, L.) 



Root-rot {Thielavia basicola, Zopf). — This fungus is found on a 

 great variety of host plants and its growth on the roots of tobacco 

 may be taken as illustrative. It is found in the eastern United States 

 and in Europe from England to Italy. Roots attacked by this fungus 

 do not develop normally and the roots may be so injured, that if the 

 plant is pulled out of the soil everything will remain in the soil except 



