yi8 Journal of Agricultural Research voi.xx.no.s 



(4) Smudge is confined to the scales and neck of the bulb, where 

 it causes dark green to black spots. On fleshy scales it appears as sunken 

 yellowish spots which enlarge slowly, coincident with gradual shrinkage 

 of the scale. On colored varieties the disease is confined to unpig- 

 mented portions of the outer scales of the neck of the bulb. 



(5) Spots on the outer scales of bulbs due to Macrosporium porri, 

 M. parasiticum, Phoma alliicola, and Urocystis cepulae may be confused 

 with smudge. 



(6) Smudge becomes detrimental to the onion crop as a cause of (1) 

 the reduction of market value of white varieties, (2) shrinkage in storage, 

 and (3) premature sprouting of sets in storage. 



(7) A detailed description of the morphology of the causal organism, 

 Colletotrichum circinans (Berk.) Voglino, is given. The ascigerous 

 form, Cleistothecopsis circinans, has been described by Stevens and True, 

 but complete proof of its connection with Colletotrichum circinans is 

 lacking. 



(8) Inasmuch as the causal organism produces a subcuticular 

 stroma and a well-defined acervulus, the species is classified in the Melan- 

 coniales as Colletotrichum circinans (Berk.) Voglino. A comparative 

 study of the latter with C. fructus (S. and H.) Sacc. was made. 



(9) The characteristic growth of the organism on culture media is 

 described. 



(10) Growth on potato agar takes place between 2 and 32 C, while 

 the optimum is about 26 . 



(11) Spore germination is stimulated in soil decoction, onion decoc- 

 tion, and sterilized soil extract, as compared with that in distilled water, 

 while it is reduced in unsterilized soil extract and entirely inhibited in 

 onion leaf or scale extract. 



(12) Spore germination occurs within the range of 4 and 32 C, while 

 the optimum temperature is from 20 to 26 . 



(13) Conidia are very sensitive to desiccation except when in spore 

 masses, in which condition a small percentage retain vitality for four 

 months or more. Stromata are very resistant to desiccation, retaining 

 vitality for two years or more. 



(14) Conidia are sensitive to freezing temperatures, but dried spore 

 masses may withstand this environment for a month or more. Stromata 

 are capable of withstanding several months of freezing weather. 



(15) The fungus is pathogenic upon the scales of mature bulbs, but 

 does not attack actively growing parts of the plant with the exception 

 of young seedlings, upon which it may cause "damping off" under certain 

 greenhouse conditions. 



(16) Spores germinate and appressoria form within 10 to 12 hours. 

 The infection tube is pushed from the side of the appressorium adjacent 

 to the host cuticle directly through the latter. The mycelium then de- 

 velops for a time between the cuticle and the subcuticular wall, raising 



