EUBBER (HEVEA; DISEASES 61 
In the case of Hevea the base of the branch rarely dies, so that 
its tissues are in intimate connection with infectious wood of the 
branch. This may lead to the gradual infection of the bark of the 
trunk by slow parasites. In this manner Diplodia theobromae^ 
Stereum umbrinum, X urn mv.l aria ardlirocodes. Ustulina, and other 
species have been found advancing on the bark of the trunk. 
All naturally pruned branches or their stubs should be removed 
as soon as possible and the surface of the exposed wood treated with 
antiseptic substances. (See " Protection of wounds." p. 66.) 
MECHANICAL WOUNDS 
Callous formations. — -The system of tapping in vogue in the Ama- 
zon Valley is responsible for more injury to the tree than all otl 
causes combined (PI. XXXI. A). The method may be briefly d< 
scribed. The seringueiro. or rubber collector, employs a small ax. 
known as a machadinho. to make the wound. With an upward 
stroke he inflicts a wound some 2 inches wide, which invariably 
penetrates the wood. As the tool is withdrawn the cortex some- 
times breaks out above the cut. exposing the wood, or the w< 
itself is splintered. The number of cuts made depends on the size 
and condition of the tree. Eight or more cuts may be made on a 
tree in one day. or the number may be less. The daily mutilation 
over a period from June to January eventually results in such in- 
jury that the tree must be abandoned. Sometimes tapping is con- 
tinued overhead, viz. beyond the reach of a man standing on the 
ground. This is usually done by erecting a platform of poles of 
varying stages around the tree. By this means the tapping may be 
carried up for many feet from the base. 
The immediate response on the part of the tree to this form of 
tapping is a vigorous effort to repair the damage. After the cessa- 
tion of the flow of lajtex. that which remains in the cut coagulates 
and for a time affords protection to the cambium and mutilated 
latex cells against atmospheric influences and infection by spores 
of fungi and insect attack. Akers. writing of the conditions in 
the Amazon, is of the opinion " that this residue of latex left in 
the cut is the salvation of the industry, when the serious injury 
inflicted on the trees from the constant use of the ax is taken into 
consideration." While the cut is temporarily sealed by the coagu- 
lated latex, the healing mechanism previously described begins the 
formation of a callus. The outer cortex at the edge of the cut 
develops a protective layer of wound cork. From the region of the 
cortical parenchyma and the bast adjoining the cambium a multi- 
plication of cells takes place. These cells continue to develop, 
usually abnormally, with the result that large irregular project- 
ing callous nodules are formed around the tapping cuts. 
The development of callous nodules around the numerous cuts re- 
sults eventually in such hypertrophy of the surface that profitable 
tapping is no longer possible. It is the formation of these cal- 
luses on a vertical series of cuts that affords one of the causes for 
giving the trees a fluted appearance (PI. XXXI. B). If the entire 
circumference is tapped the tree becomes abnormally enlarged as far 
up as the cuts have extended. This gives a bottle shape to the base 
of the tree. 
