Laffekty — Disease of Cultivated Flax. 261 



raising pure cultures from single conidia of the fungus present that the latter 

 was identical with the one used for inoculation purposes. 



The plants in the control pot remained healthy throughout the experi- 

 ment. In many cases their cotyledons lost their green colour and turned 

 yellow, but no fungus appeared on them. 



VI. — Disease Transmission. 



During the inspection of large-scale field plots of flax derived from seed 

 having different countries of origin, it was early recognized that the plants 

 from certain kinds of seed, notably that imported from Holland, were often 

 heavily attacked by " browning," while crops from seed from other countries, 

 though grown under similar conditions, often actually side by side, were 

 comparatively or quite free from it. Even before it was discovered that the 

 seed itself is liable to attack, this observation strongly suggested that 

 transmission of the disease probably took place in some way by means of 

 the seed. 



In several instances samples of the seed from which a diseased crop arose 

 in the field were obtained, and in every case it was definitely proved by 

 microscopical examination and cultural trial that such seed was infected with 

 the fungus. 



The method of seed examination for the presence of the fungus was as 

 follows : — A number of drops of water were placed on a microscope slide, and 

 a single seed from the sample under examination was placed in each drop 

 and manipulated until it became thoroughly wetted. The drops were then 

 examined microscopically with a low power. In the first few trials nothing 

 abnormal was noticed. Eventually, however, conidia identical with those of 

 P. lini were seen in abundance in the water surrounding one of the seeds ; 

 and, as the examination proceeded, numerous examples were found where a 

 similar state of affairs occurred. 



In the majority of cases where conidia were seen, the latter were present 

 in masses around the hilum of the seed, and they floated away singly or in 

 groups into the surrounding water. They were, however, by no means con- 

 fined to this region, often being present over the entire surface of heavily 

 infected seeds. 



Several of these seeds on which conidia were present were more closely 

 examined with a view to ascertaining whether the conidia were merely 

 adhering mechanically to their surfaces or were associated with internal 

 mycelium in the seed-coat. Transverse sections of such seeds when examined 

 microscopically showed that the outer layers of cells of the seed-coat were 

 permeated with hyaline, branched and septate hyphae ; and the conidia were, 



