1909 DISEASES OF GLASSHOUSE PLANTS 
the rate of about 1 part in 50 parts of water, i.e., 1 pint 
in 6 gallons. 
It will mix properly without agitation, it being 
sufficient to place it in the tank of the sprayer and run 
in the correct quantity of water. The diluted emulsion 
is best applied by means of a strong power sprayer, and 
should be carefully directed into every part of the 
woodwork, soil, etc. Special attention should be Be. 
to any rotten part of the structure. 
The ventilators should be left open while the spraying 
is in progress, so that they may be thoroughly treated, 
but must be closed down when the spraying is finished, 
in order to retain the strong vapours. The houses should 
remain closed for four days after treatment, and then 
opened to allow the vapours to escape. Fourteen days 
afterwards the house may be planted if necessary. The 
operators should wear goggles while spraying, as the 
liquid causes the eyes to smart, and rubber gloves should 
be worn to protect the hands. In high houses it is 
advisable to fit bamboo lances to the hoses, so that the 
nozzle may be held close to the woodwork and the spray 
forced into the cracks and crevices. One hundred feet 
of house, 13 feet wide and 8 feet to the ridge, requires 
about 100 gallons of spray, which takes about four hours 
toapply. Asa final precaution every cavity in the wood- 
work should be filled up with putty and painted over. 
Breeding 
It is a matter of common observation that among 
large colonies of plants exposed to infection from disease 
organisms some are completely destroyed, others only 
slightly diseased, while an occasional plant remains 
unaffected and continues to function in a normal manner. 
Such phenomena are attributed to varying degrees of 
susceptibility and disease resistance possessed by the 
individual plants. Disease resistance in a plant may be 
defined, therefore, as the ability to develop normally 
