CONTRIBUTIONS FROM THE WISLEY LABORATORY. 485 



After three days' growth, the small colony consisted of a mass of 

 intermingled hyphae which originated from the branching of the 

 main germ hyphas of the spore. The hanging drops were examined 

 every few hours to discover when spores were first produced. On the 

 morning of the fifth day a few spores were noticed which apparently 

 had been formed during the night. The conidia were not produced 

 in chains of two or three spores, as had been observed by Dowson * 

 in the case of Heterosporium Betae, but were formed singly at the tip 

 of the conidiophore, as the same author says is frequently the 

 case with Heterosporium echinulatum (fig. 106, l). After the formation 

 of the conidium, the conidiophore continues in growth and produces 

 at its tip another spore, the original spore being pushed to one side. 

 This is repeated several times (fig. 106, k). It was also observed that 

 the spores were capable of germination in situ (fig. 106, m). 



Cultures of the Fungus. — On account of the rapid germination of 

 the spores it was not a very difficult matter to isolate the fungus and 

 to establish pure cultures, but it must be stated that growth on all 

 media was slow. The fungus was first grown on beef -extract gelatine, 

 in which it formed a dense sunken mycelium and whitish aerial hyphae, 

 but owing to the fungus causing liquefaction of the gelatine at this 

 stage it was necessary to cultivate on an agar medium. The mycelium 

 produced spores when grown on the gelatine medium. When using 

 prune-juice agar and glucose agar the mycelium grew a little more 

 vigorously on the former medium. 



The sunken hyphae were brownish black in colour and the aerial 

 hyphae were light grey tinged brown, the latter colour being due to 

 the spores, which could be distinctly made out by means of a hand 

 lens of ten diameters magnification. Abundant aerial mycelium 

 was produced on the different media, and the colony formed in every 

 case became dome-shaped, but never extended over the whole available 

 area of the medium. Figs. 103, 104, represent a five-weeks-old culture. 



In slants of glucose agar in test-tubes the fungus also formed dome- 

 shaped colonies. The sunken hyphae grew rapidly, but aerial hyphae 

 and spores were not so freely produced (fig. 105). 



Infection Experiments. — ^The varieties of bearded Iris, " The Bride " 

 and " Albert Victor," which had been known to suffer from the 

 disease, were removed from the Iris beds in February and planted 

 immediately in two distinct rows on ground adjoining the laboratory. 

 It was thought inadvisable to pot the plants and conduct the 

 inoculation experiments under glass, for the reason that this section 

 of Iris is rather unsuitable for pot culture. The spores were obtained 

 from Petri-dish cultures of prune-juice agar by means of a sterilized 

 needle and dispersed in water, a few drops of which, on examination 

 under the microscope, were found to contain a good number of spores 

 as well as short pieces of hyphae. At the beginning of March five of 

 the clumps had separate cloches placed over them, three being used for 

 infection, the other two acting as controls. 



* Mycol. Centralhlatt, ii. (1913), p. i. 



