162 DISEASES OF GLASSHOUSE PLANTS 
From observations taken by the author when using trays 
(9 feet by 24 feet by 5 inches) in pairs, it was found that 
by passing steam at 60 lb. pressure into moderately 
heavy soil for 14 hours the temperature } hour after the 
steam was cut off was 210° F. at 6 inches depth, 190° F. 
at 9 inches depth, and 150° F. at 15 inches depth. The 
general practice is to pass the steam for 2 hours, thus 
allowing 30 minutes after the desired temperature is 
reached, and then to leave the boxes in position for 
+ hour after the steam has been shut off. The governing 
factor to the man in control must be the actual soil 
temperature obtained. This should be not less than 
190° F. at a depth of 6 inches. 
(d) Tank Method.—For this method a galvanized tank 
of about 100 gallons capacity is employed (Fig. 46). A 
False Wooden 
ottom. 
ee ae 
false bottom consisting of wooden boards supported on 
bricks is placed about 6 inches from the bottom and a 
piece of steam barrel fitted into it, so that steam maybe 
introduced into the space between the true and the false 
bottoms. When the tank is almost full of soil a lid is 
fitted and a tarpaulin thrown over the top. Steam is 
then passed for half an hour, after which time it is shut 
off and the tank emptied. This method has the advan- 
tage that every piece of soil is removed and sterilized 
and there is little chance of any being missed. 
