80 HATCH EXPERIMENT STATION. [Jan. 



Practical lettuce growers resort to various methods in order 

 to contend with this foe, but none of them have proved wholly 

 effectual. Most of them recognize the fact that the source of 

 contamination is largely in the soil, and that the disease is 

 much more troublesome in old soil than in new. This is 

 what might be expected, especially when the old decompos- 

 ing roots are left in the soil, as they often are, thus offering 

 the most favorable conditions for the spread of the disease. 

 As a means of controlling it, some growers have resorted to 

 changing the soil, with bcneticial results ; while others make 

 a practice of covering the surface with a layer of pure sand 

 or yellow subsoil, about one inch in depth. The burning 

 of sulphur in the house before a new crop is set is also 

 practised, and this might be expected to kill the spores with 

 which it comes in contact ; but it is ver}'- doubtful whether 

 the sulphur affects the spores in the soil to an}'- great extent. 

 It appears, however, that sulphur penetrates the soil some- 

 what, and, on account of the injury which young plants are 

 known to receive from sulphur, they should not be set for a 

 few days after it is used. 



The disease appears to be more common than formerly, and 

 this is partially due to the practice of running high night tem- 

 peratures. The collapse of the plant is most likely to occur 

 during the night, and with a lower night temperature — for 

 example, one not exceeding 38° to 40''r. — the trouble would 

 no doubt occur less frequently. The opportunities for treat- 

 ing the soils with chemicals do not appear to us to be very 

 promising, for the reason that solutions which w^ould be likely 

 to cause the death of the fungus would have to be used in 

 very large quantities, as well as much stronger than in ordi- 

 nary cases, and they would be likely to cause injury to the 

 crop. My experiments in applying a great variety of chemi- 

 cals to the soil have shown that, while a comparatively weak 

 solution accomplishes all that can be desired in the labora- 

 tory, when applied to the soil the effect of even much stronger 

 solutions more copiously applied is radically different. So 

 long as the tendency is to force crops more and more, it 

 nuist be expected that the gardener will have numerous ab- 

 normal conditions to contend with. 



No doubt the most successful and I believe the cheapest 



