186 DISEASES OF GLASSHOUSE PLANTS 
In small nurseries a small portable machine holding 
about 12 gallons of spray will be found most convenient. 
These may be taken into the houses, and a short length 
of hose will enable one of the operators to work along 
the rows of plants while another works the machine. On 
larger nurseries a motor driven machine placed outside 
the house is convenient. The spray is delivered through 
two or more long hoses taken into the house. To be 
efficient the spray must be carefully applied to each 
plant, and should be directed towards the lower surfaces 
of the leaves before spraying the upper surfaces. If the — 
upper surface is sprayed first the leaves tend to drop 
and it becomes increasingly difficult to spray the lower 
surface. At the best, spraying plants in glasshouses is 
a difficult and somewhat unsatisfactory process, because 
of the difficulty of reaching every part of the plants 
when they are close together and the foliage is dense. 
It is of considerable assistance if the foliage can be 
suitably thinned out before spraying, especially in the 
case of cucumbers and tomatoes. 
It must be remembered that spraying does no more 
than destroy the fungal parts on the outside of the plant 
and prevents further infection through the poisoned 
surface. It does not destroy those parts of the fungus 
within the tissues which later grow out and produce 
new spores. Where plants such as the cucumber are 
growing rapidly, new leaf areas unprotected by the 
fungicide are continually being produced, and may be 
infected by any spore which may settle there. This 
state of affairs may only be prevented by spraying at 
exceedingly short intervals. As this is undesirable and 
may be impracticable, special methods must be adopted. 
These consist of spraying and next day removing all 
infected leaves. About a week later the spraying and 
removal of diseased leaves should be repeated. This is 
generally sufficient to check a normal attack, but in 
severe cases it may be necessary to repeat the process 
again. 
