DISEASES DUE TO BACTERIA 127 
inner tissues of the leaf by means of the stomata, and as 
they are open during the day and generally closed at 
night, the greater part of infection occurs during the day. 
Much the same process takes place on the fruit, and the 
small, circular spots turn white in the centre and crack. 
The lesions themselves are quite shallow, but the cracking 
of the surface opens up wounds for the entrance of other 
organisms, and a rapid soft rot frequently occurs. The 
disease organisms are disseminated by the workers, 
currents of air, overhead damping, and probably by 
insects. Conditions of high humidity above 80 per cent, 
such as occur during the early morning, are conducive 
to the rapid progress of the disease, and under these 
conditions the bacterial exudate beneath the spots 
becomes abundant. Carsner reports that there is sub- 
stantial evidence that the disease may be transmitted by 
the seed ; and while the shallow nature of the fruit lesions 
would indicate that seed is rarely infected under natural 
conditions, the present-day methods of seed extraction en- 
courage such infection. No one variety of cucumber has 
proved more resistant to the disease than any other. 
Control.—The causal organisms have been found upon 
the seed, sheltering chiefly in the micropylar opening. 
Carsner recommends sterilizing the seed in 1-1,000 
mercuric chloride for five minutes as the best method 
of control. 
_ Inthis country dusting with sulphur powders or spray- 
ing with liver of sulphur and flour paste has provided a con- 
venient method of checking the rapid spread of the disease. 
‘¢ Stripe ’’ Disease of the Tomato 
The disease of tomatoes known to the nurseryman 
as “stripe ’’ (see Frontispiece) is characterized by brown, 
longitudinal markings or stripes on the stem, by shrivelling 
of the leaves, and by sunken, irregularly shaped pits 
usually of a brown colour on the fruit (36). It is a 
specific communicable disease due to a bacillus which 
