THE FUNGI WHICH CAUSE PLANT DISEASE 255 



yellowish-olive, continuous when young but at length septate, 

 30 X 7-9 n. 



Its hosts are apple and other pomaceous fruits except the pear. 

 Conidia of special form have been known under the name Napi- 

 cladium soraueri. 



The two last conidial forms have been long regarded as identical 

 and are found in literature as Fusicladium dendriticum. The 

 olive-green myceliiun in both cases grows subepidermally in the 

 leaf and fruit killing the epidermis and forming subepidermal 

 stromata from which conidiophores are produced. Stromatal 

 development is also said to be often subcuticular, resulting in a 

 separation of the cuticle from the epidermis. 



The conidia are produced apically on short stalks and as each 

 conidium is cut off the conidiophore grows forward, leaving scars 

 equal in number to the conidia produced. Pycnidia have been 

 reported on the mycelium in twigs in winter.^^* 



Perithecia first form on the lower leaf surface in October and 

 mature in April. They are most abimdant when protected by 

 sod or piles of leaves, and appear as small black pustules often 

 on grayish spots. Their connection with the conidial stage was 

 first shown by Aderhold ^^^ and confirmed by Clinton.^''' 



The fungus from apple was cultured on apple-leaf-agarby CHnton. 

 Pure colonies developed in 4 to 5 days and infection was secured 

 on leaves. Cultures from ascospores gave rise to typical conidia. 



V. crategi Aderh. occurs on Crataegus. 



V. cerasi Aderh. (=Fusicladium cerasi) is found on cherries. 

 Aderholt ^^^ demonstrated the connection between the ascigerous 

 and conidial forms. 



V. ditricha (Fr.) Karst. (= Fusicladium betulae) is found on 

 birches; V. tremulse Aderh. (= Fusicladium tremulae) on aspen; 

 V. frazmi Aderh. (= Fusicladium fraxini) on ash; 



V. inaqualis var. cinerascens Lin. (=Fusicladium orbiculatum) 

 on Sorbus. 



Didymella Saccardo (p. 251) 

 Perithecia covered, membranous, globose-depressed, minutely 

 papillate; black; asci cylindric or clavate- spores ellipsoid or 

 ovate, 2-celled, hyaUne; paraphyses none. 



