42 Diseases of Greenhouse Crops 



should be left between the 2x4 cross pieces to allow 

 for the ascent of the steam (fig. 8, a, b, c). 



When the bottom has been laid, the soil which 

 was removed can be thrown onto the platform. 

 Boards should be staked around the sides of the 

 platform to retain the soil. This forms a kind of 

 wagon box. The steam can then be turned on, ther- 

 mometers placed in the soil and the entire pit cov- 

 ered with any suitable covering to retain the heat. 



Since steam rises, this method is much more satis- 

 factory than where it becomes necessary to force the 

 steam downward. There is no puddling of soil, 

 even at the lower pressures, and 212 degrees F. and 

 higher temperature can be obtained when steriliz- 

 ing 12 inches of soil. It should be remembered 

 that a few inches of soil below the wooden platform 

 is likewise sterilized in this process. The skeleton 

 platform is easily removed by means of an iron bar 

 with a hook at the end for catching hold of the 

 2 X 4's and jerking them from underneath the soil. 

 When the framework has again been set and the 

 steam pipes adjusted in place, the platform is ready 

 for the second batch of soil, which is dug immedi- 

 ately adjoining the soil which was just sterilized. 

 In order to avoid extra labor, it becomes necessary 

 to have one pit already dug just ahead of the bed 

 being sterilized, so when the 2 x 4's are removed 

 they can be laid immediately in the pit which is 

 ready for them. This is accomplished by erecting 

 the second bed on top of the first one, i.e., on top 

 of the soil just sterilized. 



