72 BULLETIN 1380. U. S. DEPARTMENT OF AGRICULTURE 
The cause for the alteration in the latex system has not been ex- 
plained. Whether the nodules are initiated from, the modification 
of the latex vessels or from the accumulation of irritating bodies 
in the cortex the response is the same. The tree makes an effort to 
cast out the centers of irritation or surround them with protective 
tissues. Since nodules are rarely formed in the cortex of normal or 
untapped trees, it would seem that their origin must be traced to 
certain stimuli set up by injury to the bast and cortex. For this 
reason the nodules are common on trees that have been subjected to 
abuse by tin 1 tapping ax. Small pealike nodules were found on the 
renewing bark at Manaos, where the eastern tapping method had 
been employed (PL XXIII, B). The nodules were present on the 
trees at Para attacked by brown-bast. In this case the nodules de- 
veloped around disorganized tissues in the thin laticiferous layer 
immediately adjoining the cambium. 
Akers makes the statement that he is convinced that these excres- 
cences in the Malay Peninsula are the result of suppressed bud ex- 
pansion. He later quotes Huber as holding the same view and as 
stating also that they may be induced by action of hot sunshine on 
renewed bark. These views, however, are not applicable in the 
present instance. 
The severe tapping to which the trees in the Amazon Valley are 
subjected is undoubtedly responsible for the several forms of nodule 
development described in the foregoing pages. The final result is 
that the entire surface of the trunk within reach becomes so gnarled 
and irregular that it is no longer practicable to tap the tree either 
by the eastern or the local method. The bark over the plates and 
nodules is usually thin and difficult to tap without further injury to 
the cambium. It was frequently noted that the latex from the cortex 
on these nodules was of a peculiar yellowish color, quite unlike that 
of the normal parts of the tree, and coagulated more rapidly. 
Although it is undoubtedy true that the local tapping method is 
the cause of the excessive development of nodules and induces the 
various t}^pes described, a few cases have been noted where trees 
tapped at the same time as those producing nodules remained free 
from nodules of any kind. If there is any probability that certain 
strains of Hevea do not respond to injury by the production of cal- 
luses and nodules, the fact should be considered in the selection of 
seeds and bud wood. 
All nodules, regardless of their origin, when not attached to the 
wood should be removed. This may be done by lateral pressure with- 
out injury to the cambium. When attached to the w T ood by one or 
more points a slight blow will break them loose. Larger nodules 
may be cut out. if thought desirable, and the wound smoothed over 
and painted with antiseptic substances. 
ABNORMAL EXUDATIONS OF LATEX 
The exudation of latex from the cortex attacked by various fungi 
has been recorded in preceding pages. Xot infrequently latex is 
found exuding from green fruits and twigs, brandies, and trunks 
without any apparent cause. In the case of the attack by fungi the 
mechanical injury to the tissues may cause either a flow 7 of latex from 
