48 DISEASES OF GLASSHOUSE PLANTS 
produce a soft, sappy type of plant predisposed to 
disease. 
On the other hand, all diseases are not affected in | 
this way, as instanced by the Verticilliwum wilt of the 
tomato, which is more destructive to hard, underfed 
plants than to the softer rapid growing types produced 
by abundant nitrogen. 
Phosphates have the effect of inducing the production 
of abundant fibrous roots, and are generally regarded 
as causing an increased resistance to disease, but in this 
respect they are not nearly so effective as potash. 
Many cases might be quoted in which potash-starved 
plants have shown a strong susceptibility to disease, 
which has been readily corrected by suitable dressings 
of potash salts. At Rothamsted the potash-starved 
plots of wheat and mangels show a marked susceptibility 
to rusts and other diseases, while in the glasshouse 
tomato industry it has been found that potash manuring 
is necessary to keep many fungus and bacterial diseases 
in hand. As previously shown, tomato plants attacked 
by “Stripe ” disease can be made to grow away clean by 
feeding them with sulphate of potash. 
Lime is used in cultivation to “sweeten” the soil 
and is generally considered to be beneficial. It is 
especially useful on acid soils and those rich in humus, 
where its addition serves to neutralize the acidity. It is 
a common belief that the addition of lime to em soil 
assists in controlling disease organisms; and while this 
is usually true, it should be borne in mind that some 
diseases are increased by liming. Thus, before applying 
this treatment for the purpose of disease control it is 
necessary to know its effect upon the disease in question. 
Soft rot of the calla lily caused by Bacillus carotovorus 
is increased by treatment with lime or lime water, as is 
‘“‘ damping-off ” of tomato seedlings due to Phytophthora 
cryptogea or Ph. parasitica. On the other hand, both 
the Fusarium and Verticiilium wilts of the tomato are 
reduced by treatment with caustic lime in the winter. 
