362 Scientific Proceedings, Royal Dublin Society. 



or less completely disappeared, leaving the central, woody cylinder bare. 

 In such cases the stem lies more or less parallel with the surface of the 

 ground, but with its younger, positively heliotropic portion directed more 

 or less vertically upwards. Plants affected in this way may remain alive for 

 some little time, but their leaves gradually become yellow, and they die. 



If affected seedlings be examined with the microscope, especially after a 

 period of about twenty-four hours' incubation, at room-temperature, in a 

 moist atmosphere, the surface of the diseased areas, both on leaf and stem, 

 are seen to be dotted over with minute fungus pustules (acervuli). These 

 consist in the main of aggregations of conidia, and they vary in colour from 

 shell-pink to salmon. From the base of each acervulus arise, not only the 

 short conidiophores, on which the single-celled conidia are borne, but also 

 a number of characteristic long, black, tapering hairs or setae. (See fig. o, 

 Plate XIX.) 



Sections through the diseased tissues show an abundance of fungus 

 mycelium in them, but in no case have any indications of the formation of 

 sclerotia been observed. 



The conidia are hyaline, non-septate, rounded at each end, and either 

 cylindrical or slightly fusiform in shape. Each contains a central oil-drop. 

 In breadth they vary but little, measuring iisually about 4/x in this direc- 

 tion. There is, however,- considerable variation in their length. The 

 extremes found were ll^u and 21ft, whilst the average length of fifty conidia, 

 taken at random, was 17ju. 



The conidiophores are short, unbranched, and hyaline. They arise from 

 a small sub-epidermal aggregation of hyphae, scarcely developed enough to 

 be regarded as a definite stroma, and are compacted together in the form of 

 minute tufts, which break through the epidermis of the host, and protrude 

 to a very short distance beyond it. The conidia are formed only after the 

 epidermis has thus been broken through ; and no case has been met with of 

 conidia being borne actually within the host- tissue, as has been described by 

 Atkinson 2 for Colhtotriclmm yossypii. 



The setae arise from the same source as the conidiophores. They are 

 dark -brown to black in colour, except at their more or less hyaline, tapering 

 apices. They are usually three-septate, and the basal cell is ofteu some- 

 what swollen. They vary considerably in length, but, on an average, are 

 150/x long and Aft broad. Two to ten of them may be present in each 



1 The colour nomenclature adopted in this paper is based on Ridgway's "Colour 

 Standards and Nomenclature." Washington, 1912. 



2 Atkinson, G. F. Anthracnose of Cotton. Joum. Mycol., vol. vi, 1891, p. 173. 



