FORMATION OF NODULES. 
285 
abundant deposit of tannin in the adjacent cells, and the 
arrangement of the cells in the covering layers as in the callus 
in wounds. Latex may ooze out and coagulate on the exposed 
surface and later be included within the covering layers, and 
thus give the structure a fictitious resemblance to a nodule. 
Large nodules in their development may meet with globular 
shoots, or may stimulate dormant buds to activity. These 
fuse with the tissue of the nodule on coming into contact with 
it, and later throw out vascular projections towards the stem 
wood. In some cases vascular projections might already be 
present when fusion occurred with the nodule. This does not 
account for all vascular connections of nodules, as in some 
nodules the vascular connection can be traced right into the 
altered latex vessel region of the core. It is possible, however, 
that even in these cases, at the inception of cell division near 
the altered latex vessels, a bud primordium was present, or 
that the cortical cells on being stimulated to activity developed 
bud or shoot characters. 
Globular shoots never develop into large masses of woody 
tissue. The largest specimens obtained measured approxi- 
mately I inch in diameter. 
General. 
Isolated wood bodies occur in the cortex of other trees. 
Sorauer’s investigations (19, p. 183) on nodules in apple trees 
showed that the central core consisted either of hard bast 
elements or of cortical parenchyma cells ; the outer layers of 
wood elements were similar in structure to the wood elements 
of Hevea nodules. Sorauer was of opinion that apple nodules 
arise as a consequence of wounding, as they are readily formed 
in the vicinity of wounds. He describes short woody strands 
which he found in the cortex of pear trees ; these had a central 
core as in apple nodules, but the wood elements were arranged 
parallel to those in the adjacent wood. Sorauer considered 
these strands to be new formations. 
Krick (15) minutely described the woody nodules found in 
the cortex of the beech, and distinguishes two types : (1) 
nodules bearing buds or shoots ; the wood of the bud or shoot 
can be traced continuously right through into the nodule ; 
