DISEASES DUE TO FUNGI 61 
soon destroy the wood. A contaminated source of water 
is more difficult to purify, but the general method will be 
treated in a later chapter. Frequently the propagating 
soil becomes contaminated by a chance infection, which 
is not realized until the disease reaches the epidemic stage. 
Such cases have emphasized the necessity of devising 
methods of checking the disease when it appears, and as 
the result of investigations (6) at the Cheshunt Experi- 
mental Station it was found that a solution of a mixture of 
copper sulphate and ammonium carbonate will do this, 
The mixture, which for convenience has been named 
“Cheshunt Compound,” consists of two parts by weight 
of copper sulphate and eleven parts ammonium carbonate. 
The ammonium carbonate, which must be fresh, is reduced 
to a fine powder by crushing out the lumps. It is then 
thoroughly mixed with powdered copper sulphate in the 
correct proportions, and stored for twenty-four hours in 
a tightly corked glass or stone jar before using. The 
solution is prepared by dissolving one ounce of the dry 
mixture in a little hot water and adding to two gallons of 
water. It should not be put into vessels of iron, tin, or 
zinc, as it corrodes them and loses its strength, and 
just as much as is required for immediate use should be 
prepared. Plants may be watered with this solution 
without injury, while the “ damping off” organisms in 
the soil are destroyed, but infected plants receive no 
benefit from the solution, for the fungus is already inside 
the tissues where the liquid cannot reach it, and such plants 
eventually die. The seed-boxes should be thoroughly 
watered with the solution after sowing and covering the 
the seeds. When potting up, the seedlings should be 
watered first with the solution while still in the boxes, 
to ensure that the roots are thoroughly wetted, and 
after transplanting into the pots the solution should 
again be applied. To enable sufficient solution to be 
given to each plant the level of the soil should be one 
inch below the level of the pot. The solution may be 
used in the houses by adding a pint to each of the holes 
