194 DISEASES OF GLASSHOUSE PLANTS 
Similar benefits result when hygienic methods are applied 
to glasshouse work, and it is in the interests of the 
grower and the whole country that cleanliness should 
prevail in every nursery and market garden. Contami- 
nated soil, manure, water, seed, imported plants, and 
weeds are important sources of infection, as are also 
contaminated buildings, market baskets, workers, visitors, 
and insects. It is important to realize this, for in every 
case a little knowledge before the event is better than a 
good deal more afterwards. Often growers are reluctant 
to spend time and money in destroying weeds outside 
the houses, but it is always worth the expenditure, and ~ 
where centres of infection are known to exist no pains 
should be spared in their elimination. 
(b) Cultural Methods.—The wise grower has learned 
by experience, often dearly bought, that plants which 
are grown strong and vigorous, without any tendency 
to soft, sappy growth, are often resistant to many 
diseases. So obvious is this fact to the observant 
grower and pathologist that no study of a particular 
disease can be complete unless a study of the effect of 
different cultural conditions upon it has been made. 
The rapid forcing of glasshouse produce so that early 
markets and high prices may be captured often ends in 
producing plants susceptible to disease, while a healthy 
growth, developing uniformly, often produces plants 
upon which disease can make no headway. Cultural 
details are vastly important, and there is an immediate 
need for investigation, so that when a particular disease 
appears the best conditions for assisting the plant in its 
struggle for health and life are known and can be applied. 
Spraying, Dusting, and Sterilization 
In cases where the disease has got the upper hand 
and cultural means are ineffective or unknown, the above 
devices must be resorted to, but they require careful 
application, and frequently are difficult to carry out. 
