Laffkkty — Disease of Cultivated Flax. 267 



in so far as they could be reached from the headlands ; and such portions 

 might possibly be sufficiently large to provide the requisite quantity of seed 

 in a given case. But until it can be done from the air by a hovering 

 aeroplane, or by a dirigible airship, or other such means, spraying a flax crop 

 at such a time will not be a practicable proposition, since with present-day 

 machinery the injury which would follow the trampling down of the crop 

 would be irreparable. In addition to this, there is to be considered the effect 

 which tlie adhering fungicide might have on the subsequent process of 

 retting. Whether spraying at a much earlier stage would be feasible without 

 injury, and, if so, whether it would be effective in preventing " browning," 

 is a problem which has yet to be explored. 



Mechanical Avoidance of Infection from Seed- coats. — Since primary infection 

 occurs in the seedling stage, and is due to the transfer of the parasite from 

 the infected seed-coats to the cotyledons, on which the former are borne 

 above the ground, it might be thought possible to intercept such primary 

 infection by preventing the carrying aloft of the seed-coats ; that is, by 

 deep sowing of the seed. 



Healthy seed was sown in plots at depths varying from half an inch to 

 three inches ; but it was found tliat sowing at a greater depth than one inch 

 resulted in the production of such a thin braird of weak seedlings that a 

 reasonable crop was quite out of the question. Moreover, it was also found 

 that sowing infected seed at a depth of one inch did not suffice in many cases 

 to prevent the seed-coats being carried up on the cotyledons, and infection of 

 the seedlings was found to occur under such conditions. Hence, control of 

 the disease by deep sowing of the seed is out of the question from a practical 

 point of view. 



Seed Disinfection. — Considerable attention has been devoted to the 

 question of disinfecting affected seed both by means of fungicides and by 

 heat'; and a summary of what has been done along these lines will now be 

 given. At the outset it may be remarked that fiax presents special diffi- 

 culties in regard to tieatment with most fungicides in solution or suspension 

 in water, owing to the mucilaginous nature of the outermost layer of the 

 seed-coat, and the tendency of the treated seeds to adhere together in a 

 sticky mass when wetted, thus rendering sowing extremely difficult or quite 

 impossible. Experiments are in progress with a view to finding a way out 

 of this difficulty, but they have not yet been carried sufficiently far to 

 warrant discussion here. 



Preliminary trials were made with aqueous solutions of copper sulphate 

 and mercuric chloride, as well as with Burgundy mixtures (copper sulphate 

 and sodium carbonate solutions) of varying strengths. Formaldehyde both in 

 aqueous solution and in gaseous form was also tried. Sufficient seed to sow 



2n 2 



