78 Scientific Proceedings, Royal Dublin Society. 



paratively easy matter to obtain it in pure culture. This has been done 

 in several instances by planting out the conidia in gelatine media either 

 directly or after a first transference to suitable slants in test-tubes, or to 

 media previously allowed to set in Petri dishes. In this last-named way it 

 is possible to exercise microscopic control over the growth which develops 

 from the inoculating material ; and platings of conidia from growths of this 

 kind, which are found to be free from bacterial or other contamination, have 

 always given pure cultures. In some instances the additional precaution 

 was taken of making successive platings before arriving at the particular 

 culture destined to serve as a stock from which cultural and other studies 

 were to be made. 



The fungus has also been isolated from the vascular tissue of affected 

 tubers both before planting and after they have been planted and have 

 given rise to diseased plants. It frequently happens that the parent tubers 

 from which diseased plants are developed are to be found at the close of the 

 season more or less completely hard, sound, and not fully depleted of their 

 reserve food materials. In such tubers the woody tissues containing the 

 fungus are strongly browned, as shown in fig. 3, Plate III. Cultures from 

 tubers were obtained by transferring — under conditions of asepsis — portions 

 of the affected woody tissue direct to suitable media in slants or on set plates. 

 Some of these direct transfers proved to be pure from the start, while others 

 of course were contaminated by the presence of other organisms, especially in 

 the case of old tubers ; but even in these latter instances Verticillium albo- 

 atrum was always present, and by further work could be obtained in pure 

 culture. 



The fungus grows well as a saprophyte on a variety of media such as 

 Quaker Oat agar, oat-extract agar, wort gelatine, cooked potato agar, potato- 

 stalk agar, cooked potatoes, cooked potato-stalks, and beef extract agar and 

 gelatine. 



It produces both aerial mycelium bearing conidiophores with conidia and 

 submerged mycelium. There has been a tendency during the period of over two 

 years through which the cultures have continuously been propagated for the 

 relative proportion of aerial mycelium developed to diminish. Both the aerial 

 and the submerged mycelium is at first pure white in diffused light, but in 

 the course of time black submerged mycelium is produced just in the same 

 way as occurs in the stalks of affected plants, and the medium therefore 

 becomes blackened. This blackening is due solely and entirely to the 

 blackening of the mycelium, and not to the production of dark chlamydo- 

 spores, as occurs in the two other species of Verticillium already 

 alluded to. 



