Lafferty — Disease of Cultivated Flax. 263 



was concluded on the thirty-third day after planting, and out of a total of 

 forty- six plants fourteen showed diseased cotyledons. As the seedlings had 

 not been watered, and the bell-jar was not removed before the appearance of 

 the disease on the cotyledons, their infection must have resulted from the 

 fungus present on the seeds sown. 



Diseased cotyledons from the infected seedlings were examined micro- 

 scopically, and it was found that the brown tissues were filled with hyaline, 

 septate, and branched hyphae, while groups of conidiophores were bursting 

 out through the stomata and producing conidia in typical acervuli of P. lini 

 on the surface. Isolations of the fungus, starting in each case from a single 

 conidium from one of these acervuli, were made, and in every case it proved to 

 be identical with the species found on the leaves, stems, fruits, and seeds of 

 browned plants. This experiment shows that the disease is capable of 

 transmission by means of infected seed. 



As is well known, iJax seeds when sown and lightly covered with soil 

 germinate, and in a great many cases their seed-coats are carried above soil- 

 level, attached more or less loosely to the cotyledons. Where infected seeds 

 are sown it is obvious that the infection of the cotyledons may take place 

 from the fungus present on the seed-coats borne aloft in the manner 

 described. In the experiment described above a record was not kept of the 

 number of seedlings which carried up their seed-coats, biit, as the seeds were 

 planted approximately one inch deep, the number must have been small. 



In the spring of 1919 flax seeds from a sample which had produced a 

 browned crop in 1918, and some of which were proved by microscopical 

 examination to be infected, were sown out of doors in a plot attached to the 

 field laboratory. 



When the plants had brairded, many of the cotyledons of the seedlings 

 showed the presence of one or more brown circular spots, which on incubation 

 in a moist atmosphere produced acervuli typical of the " browning " fungus. 

 From conidia present in the acervuli, /*. lini was isolated and grown in pure 

 cultures. Such diseased areas on the cotyledons, some of which are illustrated 

 in fig. 1, Plate VIII, were thus found to be the incipient stage of "browning" 

 as it occurs in the field. 



Cotyledons attacked by P. lini resemble very closely those attacked with 

 " seedling blight," and in some cases the two diseases at this stage can only 

 be differentiated with the aid of a microscope. To the naked eye the injury 

 due to the " seedling blight " fungus {Colletotrichu7ii linicolum) is lighter in 

 colour than that due to P. lini, and its progress is also more rapid. In the 

 former case an infected leaf soon becomes entirely destroyed ; and this is 

 often- followed by death of the seedling as a whole, owing to the formation of 



