FORMATION OF NODULES. 
265 
the decomposition of the contents of these latex vessels. In 
the course of tapping latex vessels may be severed above and 
below, and the latex in the remaining portion may coagulate 
or decompose and so inaugurate nodule formation. The latex 
does not appear to coagulate in the latex vessels, but rather 
seems to exude into the surrounding cells. The authors admit 
the difficulty that only a few leaf traces give rise to nodules, 
and only a few stems tapped or untapped have nodules present ; 
their theory would require nodule formation to be the rule 
rather than the exception. 
Keuchenius (14) in 1914 discussed the effect of the pricker 
in inducing the formation of nodules, and came to the conclu- 
sion that the pricker was the chief agent, but that nodules 
might also be formed as the result of injury from fungus or 
insect attack. The pricker, especially if the teeth are blunt, 
tears the cortex and pushes cells bodily out of position. The 
pricker marks are healed up in the usual way ; a cambium 
forms round them, which produces cork cells externally, and 
so closes the wound in the cortex. The bodily displaced cells, 
however, become a source of irritation to the surrounding 
cells, which then begin to divide, and so give rise to a nodule. 
It can, however, no longer be maintained that the pricker is 
even the chief cause, as the pricker has fallen into almost 
complete disuse ; yet nodules are found on many trees now in 
tapping, but to which the pricker has never been applied. 
Bateson in 1914, in a later Bulletin (7), expands his theory of 
the origin of nodules. He states that “ Coagulation of latex 
inside the vessels takes place normally in the outer cortex, 
and does not apparently give rise to burrs. From this it may 
be inferred that the cells of the outer cortex have lost their 
power of responding to this particular stimulus by forming 
a cambium ; the cells of the inner cortex being younger are 
probably more easily stimulated into a resumption of cambial 
activity.” From the evidence adduced later it will be seen 
that this statement is open to some doubt, as inception of 
nodule formation was observed to occur almost invariably in 
the outer cortex. 
Bateson cites three causes which may lead to the isolation 
of latex vessels, stagnation of movement of the latex in the 
6(14)17 (37) 
