268 
BRYCE ! 
and of the nodule is irregular, corresponding mth irregu- 
larities on the adjacent cortical surface, the condition being 
due to unequal cambial activity under the abnormal state of 
the tissues. The surfaces of nodules are marked with raised 
ridges running in parallel undulating lines and in places 
describing whorls. Similar raised undulating lines can be 
traced on the stem wood in many instances. 
On cutting into nodular cortex, pockets or cavities of several 
inches diameter containing rubber are frequently encountered ; 
occasionally these are lenticular in form. Fetch (23) states 
as follows : “I have taken three ounces of almost dry rubber 
from such a situation.” These cavities may have been formed 
by the rupture of the cortex under the internal strains set up 
by the developing nodule. Latex would then flow from the 
ruptured latex vessels into the cavity and would coagulate 
there. Such pockets of rubber are likewise found in trees 
subsequent to attack by parasitic fungi, more particularly 
after attacks of canker {Phytophthora Faberi). 
Nodules do not extend to the parts cf the plant below 
ground ; they are not found on the roots even when these are 
exposed to the air, though the stem may be badly affected 
down to the ground level. 
Nodule formation appears to spread out in all directions 
over the stem from the point of origin. ^ 
Untapped trees up to eleven years old have been examined 
in large numbers, but not one case of large, massive nodular 
growths has been found by the writer on such trees. 
Structure. 
Transverse sections of nodules show three zones of tissue 
{a) A central core, dark brown in colour, appearing as a 
point or line. It consists of cortical elements, and represents 
that portion of the original cortical tissue round which cambial 
activity started in the formation of the nodule. 
(6) Surrounding the core is a zone of wood elements derived 
from the nodule cambium. These form the bulk of the 
substance of the nodule. 
(c) On the outside is the nodule cambium with the few 
cortical cells which it cuts off externally. 
