168 "Damping off" etc., of Tomato Seedlings 



for 48 hours, and allowed to stand uncovered for 10 days to make sure all 

 the formaldehyde has evaporated. The seed is then sown in the usual 

 manner. So long as the water is not infected this treatment will ensure 

 a healthy batch of seedlings. 



The Seed-box as a Carrier of Disease. 



Twenty-four boxes in which "damping off" had been very severe 

 were used. Twelve were left untreated as controls and the remaining 

 twelve were soaked for ten minutes in a 2 per cent, solution of formalin 

 contained in a tub. They were then placed in a heap and covered with 

 sacking for 48 hours in order to allow the vapours of the formaldehyde 

 to act upon the fungi present in the boxes. After this time the sacking- 

 was removed and the boxes allowed to dry. All the boxes both treated 

 and untreated were then made up with sterilised soil, sown with sterilised 

 seed, watered with sterile water and placed on sterilised glass plates in 

 the greenhouse. The plants grown in the sterilised boxes were perfectly 

 healthy and showed no signs of "damping off," while eleven boxes out 

 of twelve untreated showed an average of 14 per cent, diseased seedlings. 



The results of this experiment, which are given in Table VIII, show 

 that seed-boxes carry the infection from one season to another. 



Table VIII. 



Date Untreated boxes Treated boxes 



7. 8.19 Seed sown Seed sown 



20. 8.19 One box showed disease All boxes with healthy plants 



30. 8.19 Five boxes showed disease „ „ „ 



7. 9.19 Nine boxes showed disease „ , „ 



23. 9.19 Eleven boxes showed disease Two diseased seedlings in one box 



7.10.19 Eleven boxes showed disease „ „ „ 

 One box with healthy plants 



The Pot as a Carrier of Disease. 



Twelve pots which had previously contained plants attacked by 

 "foot-rot" were obtained from a nursery. Six were treated with a 

 2 per cent, solution of formalin in the same manner as the boxes in the 

 previous experiment, while six were left untreated to serve as controls. 

 In four of the six untreated pots the plants developed "foot-rot," while 

 in all the six treated pots the plants remained perfectly healthy. 



Sterilisation by formaldehyde of the soil in heaps. 



The soil used in the experiment was naturally infected soil obtained 

 from a nursery; and when tested was found to produce the disease quite 



