Pethybridge and Lafferty — A Disease of Flax Seedlings. 363 



acervulus. No cases either have been observed where setae perform the 

 role of conidiophores, such as have been described for 0. gossypii. 



From what has been said it will be evident that the fungus present on 

 the affected flax seedlings belongs to the genus Colletotrichum, and in order 

 to study it in more detail, and to ascertain whether it was responsible for the 

 disease, it was isolated, and grown in pure culture, and infection experiments 

 were carried out. 



III. — Isolation of the Fungus and Growth in Puke Cultures. 



Since the production of conidia on the. host plant is abundant, and the 

 conidia are large enough to be located individually under the microscope, 

 it was a comparatively easy matter to get fungus into pure culture. 



Conidia- suspensions of suitable dilution were inoculated into tubes of 

 melted wort-gelatine and plated out in the usual way. After the gelatine 

 had solidified, the locations of completely isolated single conidia were marked, 

 and, after germination had occurred, the latter were removed to suitable 

 media slanted in test tubes. Thus each culture emanated from a single 

 conidium. 



The fungus grows well on a variety of media, producing an abundance 

 of conidiophores, conidia, and setae. The following are some of the media 

 used: — beef-extract-agar, and -gelatine, wort-gelatine, quaker-oat-agar, potato- 

 stalk-extract-agar, cooked potato, tomato-fruit-extract-agar, green flax-extract- 

 agar and oat-extract-agar. Gelatine media become liquefied slowly when the 

 fungus is cultivated on them. 



On beef-extract-agar the growth of the fungus is very meagre, and on 

 beef-extract-gelatine no conidia, setae or appressoria were found. On the 

 other media mentioned it varies in luxuriance with the nature of the medium, 

 but as regards morphological characters the variation of the fungus when 

 grown on the different media is very slight. 



In general the nature of the growth on these media is at first sparse, and 

 not much raised above the surface. At the outset white, it gradually turns 

 grey and finally becomes almost black, at least in that portion of it at or 

 near the surface of the slant. This uppermost dark layer consists of a matted 

 mass of dark-brown, gnarled and twisted hyphae. 



The submerged mycelium permeating the medium consists of branched, 

 septate, hyaline, hyphae ; where, however, these come into contact with the 

 sides of the test-tube in which the medium is contained, dark, irregular, 

 thick-walled cells are produced, either singly or in chains. They may be 

 terminal or intercalary, and are produced especially in media which are not 



