168 DISEASES OF GLASSHOUSE PLANTS 
40 gallons of diluted acid is applied to 9 square yards, 
but on heavy soils the same quantity is applied to 12 
square yards. The original method was to apply the 
acid in two half-strength dressings with a fortnight’s 
interval, and wash each into the soil by copious watering. 
The present plan is to spread the diluted acid over the 
soil, so as to saturate the top inch or so, and at once dig 
the ground, so as to leave the saturated layer of soil a 
foot below the surface. By so doing the vapours per- 
meate the top foot of soil and sterilize it. 
Probably the best way of applying the acid is to 
absorb it in a quantity of dried soil containing gypsum, 
which is then well mixed with the soil by digging. 
Cresylic acid has proved useful in increasing soil fertility, 
but while it reduces certain diseases to some extent it 
does not eradicate them completely. 
Sterilization with Formaldehyde 
Formaldehyde has proved eminently satisfactory for 
bringing about the destruction of some disease organisms 
in the soil, but the present cost prohibits its extended 
use on a large scale. For sterilizing a few tons of soil in- 
tended for propagation the excellent results obtained 
more than compensate for the expense. A 2 per cent 
solution prepared by adding 1 gallon of 40 per cent 
formaldehyde to 49 gallons of water will effectively 
sterilize most soils. To sterilize each ton of moderately 
heavy soil 14 gallons of 40 per cent formaldehyde or 75 
gallons of the diluted solution is used. A suitable place 
to perform the operation is first chosen, and this should 
be fairly flat and if possible protected by an overhead 
covering to keep off the rain. The ground should be 
beaten flat and damped with formaldehyde. The soil to 
be sterilized is laid out in a layer not more than 6 inches 
deep and saturated with the diluted formaldehyde. 
Another layer of soil is placed on top and saturated in 
turn, until the whole of the soil has been treated. The 
