330 THE PARASITIC DISEASES OF PLANTS 
cultures of the organism. It is the cause of considerable losses 
to horticulturists. 
Root Tubercles of Legumes.—These have been considered in a 
different connection (Chapter VII), but they are properly classed 
here. They are certainly caused by parasitic bacteria, although 
in this case apparently both the parasite and the host are benefited 
by the association, a condition sometimes called symbiosis rather 
than parasitism. 
Fic. 54.—-The crown gall on the root of the raspberry. 
Remedies.—Remedies for the bacterial diseases are not as yet 
very satisfactory. Spraying, so frequently efficient against 
fungous diseases, is of no value here, because the bacteria are 
always within the tissues of the plant where the spray cannot 
touch them. Hence in dealing with plant diseases in general 
it is always desirable to know whether they are fungous or bacterial 
since in the latter case spraying is always useless. Each disease 
has to be met by devices adapted to the peculiar nature of the 
disease, and no general principles can be given beyond that 
already pointed out on page 310. 
