266 Scientific Proceedings^ Royal Dublin Society. 



given field a second crop of flax normally follows a previous one only after 

 an interval of six or seven years. It seems scarcely likely that affected 

 stalks, left lying in the field after the first crop, could possibly be a source of 

 infection in such circumstances. It is more probable that they vifould have 

 disappeared entirely and the fungus with them. There is no evidence at 

 present, at any rate, that the fungus can live as a saj)rophy te in the soil ; nor 

 is there any eA'idence that infection of the crop comes from the soil. Again, 

 after retting, flax is spread on grass fields to dry, but such grass land is not in 

 practice laid down to a crop of flax in the following season, and often not for 

 some years. Even if a few affected stray stalks were left on such land, and 

 assuming that the fungus was not materially injured during the retting 

 process, it seems improbable that infection would occur from this source. 



The " shives " (debris consisting of woody cylinder and cortex) which 

 accumulate at scutching mills, where the fibre from the retted flax is 

 mechanically separated from the rest of the stem, are sometimes used for 

 bedding farm stock. It is conceivable that should the fungus survive the 

 retting process it might ultimately reach the land again in manure derived 

 from such material. It is believed, however, that even if it exists at all, 

 this possible source of infection is of no practical significance ; and, as has 

 been already stated, there is no evidence at present that the disease is 

 contracted from the soil. 



Ensuring Healthy Seed. — On the other hand, it has conclusively been 

 proved that " browning " and ''stem-break" can be transmitted by sowing 

 infected seed;i and it is believed that this is the most important, if not the 

 only, means by which outbreaks of the disease arise. Control measures, 

 therefore, centre around the question of the seed; and the most obvious 

 precaution would be to avoid saving seed for sowing from a crop suffering 

 from " browning." 



It might be considered possible to save healthy seed from a diseased crop 

 by pulling the latter before the fruits and seeds had become infected. An 

 attempt was, in fact, made to do this, but, owing to the early date at which 

 pulling was necessary, the quantity of seed saved was extremely small ; and it 

 was found to be altogether too immature to be of any use for sowing purposes. 



Again, it might be thought possible to check "browning" and prevent 

 infection of the fruits by spraying the affected crop with an appropriate 

 fungicide. It might, indeed, be feasible to spray the marginal portions of a 

 field of flax at the time when "browning" was beginning to become evident, 



1 Viability tests of the conidia present on infected seeds showed that they retained 

 their vitality on the dry seeds for two years and six months after harvesting. In three 

 years, however, the conidia were all dead. The germination of the seed in this period 

 had, of course, greatly diminished, 



