464 Diseases of Economic Plants 



bed and a fire built under it. The soil on one side of the pan 

 to a depth of 6 inches is shoveled and heated, great care being 

 taken to keep it moist, otherwise the humus would be burned 

 out and the physical texture seriously altered. After an 

 hour this soil is put back and that from the other side of the 

 pan subjected to the same treatment, and then the pan 

 moved along to a new place. The soil underneath the pan 

 itself is thereby subjected to heat for two hours. 



Disinfection by formalin. — The use of formalin for the 

 disinfection of greenhouse soil and of tobacco seed beds 

 against Corticium has been in vogue for some time with 

 excellent results. It furnishes a very simple means of disin- 

 fection as follows: The beds are thoroughly prepared as for 

 the other methods of disinfection described and are then 

 drenched with a 2 per cent formalin solution using two 

 quarts of this solution to the square foot of bed space. The 

 solution should be put on with a watering pot with a rose 

 orifice and distributed as evenly as possible over the bed, so 

 as to wet the soil thoroughly to the depth of a foot. It will, 

 in most cases, be necessary to put this solution on in two or 

 three applications, as the soil will not immediately take 

 in this quantity of water. The beds should then be covered 

 with heavy burlap or a tarpaulin to retain the fumes for a day 

 or so, and then aired for a week before sowing the seed. 



Spring applications of formalin are open to the following 

 objections: The addition of such a large quantity of water 

 to the soil keeps it wet and cold longer than would naturally 

 be the case, thus delaying germination as well as subsequent 

 growth; the necessity of airing the beds to remove the for- 

 malin fumes and to allow the soil to dry out also causes delay 

 in seeding. To obviate these difficulties the beds should be 

 treated in the fall, before freezing. 



Disinfection by sulfuric acid. — One-eighth to three- 

 sixteenths fluid ounce of commercial sulfuric acid in from one 

 to two pints of water, according to the humidity of the soil, is 

 applied per square foot of soil immediately after the seeds are 

 covered. This treatment is used principally for conifers. 



