10 
the presence in the juices of the plant of some substance which 
attracts the parasite. On this view infection is independent of the 
health of the plant, but it has been found that “ susceptibility can 
be induced by various kinds of mechanical injury ” a.nd also by 
certain interferences with the normaTiunctions such as :anaesthetis- 
ing or overheating the leaf. Often stem-boring insects open the 
way for hurtful fungi and bacteria. T\here i s a el ass °f fungi — the 
wound parasites — which can only obtairk^. hold on the plant when 
the bark has been injured. Animals frequently denude considerable 
areas on certain kinds of trees: tar should ibe liberally applied in 
such cases. 
The interference of man with cultivated plants is to submit them 
to conditions different in many ways from those surround! ng tile 
plants in their wild states, and to develop them along particular lines, 
thus disturbing the normal equilibrium and rendering the plant more 
susceptible to disease. This may have a lot to do with the violent 
epidemic character frequently assujned by some diseases of cultivated 
plants. 
The economic pursuit of the greater number of cultivated plants 
is for their ripened fruits, or for some part connected with repro- 
duction, such as tubers and fleshy roots. This would not appear at 
first sight to be very harmful as the production of seed is the great 
feature in the life of a plant, one might truly say the aim and object 
of its existence. But man is not content with the quality and 
quantity of seed which a plant produces in its wild state. He seeks 
to make various modifications which leave the plant more prone to 
disease. The balance of a tree’s functions is more disturbed where 
something other than the fruit is the object, such as latex in rubber- 
producing trees, and various unhealthy signs may make their 
appearance. In all trees there is a considerable power of respond- 
ing to changed surrounding and repairing injuries, but some kinds 
possess it to a greater extent than others. Tapping rubber trees 
must be looked on as an injury to the tree, but the Para rubber tree 
(Hevea brasiliensis) appears to be far from delicate and to manifest 
a great plasticity in adapting itself to new conditions, but this pro- 
perty cannot be too far presumed upon. Enough information has 
not yet been collected to specify the effect of tapping on the health 
of the tree, but on theoretical grounds the action of many Planters 
in giving the tree a couple of months’ rest, especially during the 
leafless period, is commendable and is probably necessary to restore 
the functions to their normal state. It is well known that tapping 
Rambong (Ficus elastica Roxb.) and Ceara (Manihot Glaziovii 
Mull-Arg.) after the manner practised on Para has had fatal results, 
even when the cambium remained uninjured. 
In a Para tree on the inside of the cortex, the part containing 
the latex-vessels, there is a thin layer called the bast, which is a 
kind of highway along which food products elaborated in the leaf 
travel to the root and other parts of the tree. Inside this is another 
thin layer, the cambium, which has the power of growth ; it adds to 
the wood on the inside and to the bast on the outside, thus 
