( 2 ) 
Plantation Before proceeding to deal with specific 
Conditions in crop diseases of local interest, it may 
Relation to be instructive to indicate the chief 
Rapid Spread reason why plant diseases become 
of Diseases, more dangerous when a jungle tree, 
such as the rubber tree, is cultivated 
under plantation conditions. In the natural forests 
every tree is a survivor in the struggle for existence 
and only the hardiest individuals come to maturity. 
In the jungle, the mature trees or groups of trees 
of any single species are usually separated from 
the individuals of the same species by trees of 
widely differing constitution. Specialization or 
preference for one individual host, or at most a 
narrow range of hosts, is a well-known phenomenon 
in the case of parasitic fungi, so that, under jungle 
conditions, a diseased tree may be found, but the 
fungus causing it cannot attack the neighbouring 
trees because their constitution is so widely different 
from that of the attacked tree. Plantation condi- 
tions are diametrically opposed to those of the 
jungle — the struggle for existence does not operate 
to the same extent, since each seedling plant has 
similar conditions and many comparatively weak 
individuals survive. The weak individuals may be 
attacked more easily by disease, and since each tree 
has a similar constitution to its neighbour, every 
single tree in the plantation may become infected. 
Plantation conditions, as a rule, favour rapid spread 
of disease and it is easy to realise that the greatest 
care is necessary in the case of the cultivation of 
a jungle plant taken from its native habitat. 
Diseases of Rubber. 
PRIOR to 1912 little definite research work had 
been carried out on the diseases of the rubber tree. 
