—— aae 
ON THE STEM OF DAMMARA ROBUSTA. 447 
bast-fibres, the latter forming a tortuous complex heap apper- 
taining to the woody system of the core, and, like it, arranged 
independently of the general phloóm. The cambium elements of 
the scar, therefore, it is clear, are not arranged in conformity 
with those of the rest of the stem. The cicatrix resulting from 
the common detachment of a dead branch in an exogenous tree 
and that resulting from disarticulation are readily distinguishable. 
In the first case healing is effected by a growth of callus from the 
surrounding cambium which extends over the fractured surface 
of the wood ; in the callus are differentiated a superficial cortical 
system and a deep system of modified wood. The most central 
part of the scar in such cases presents an external eminence 
which marks the central meeting and coalescence of the circular 
cicatricial growth from the margin. 
After branch-disartieulation or cladoptosis (Berkeley), the 
surface heals throughout simultaneously, or, more truly, it is 
healed before the branch is actually shed ; and the scar in this 
case, in place of being centrally convex, is concave throughout. 
Do the branch-scars in Dammara, Aspen, Oak, &c. throw any 
light on the scars occurring in Ulodendron, the nature of which 
has been the subject of so much discussion? I am afraid not. 
Indeed, when it is considered how different is the histology of 
the extinct Lycopods from that of any existing trees, it is almost 
hopeless to expect to find any existing scars identical with those 
of Ulodendron. 
In Ulodendron the scar, as Carruthers remarks, is always in 
the form of an inverted cone, generally, however, flattened 
from the enormous pressure, and more or less oval; the base or 
centre of the pit is different in different species, double horse- 
shoe-shaped, half-oval, or circular: the figure is formed by a 
number of small pits representing the number and position of the 
vascular cords which supplied the supported organ ; the remainder 
of the scar is covered with single pits or radiating furrows 
arranged in symmetrical order around the base of the scar, the 
Pits being confined to the lower half of the scar, the furrows to 
the upper half. In Dammara the scar presents a central fossa, of 
different depth in different scars, and this is bounded by a low 
Oval or horseshoe-shaped ridge which marks the situation of 
the fractured wood, beyond which is a lowly convex ring, corre- 
sponding with the cortical parenchyma of the shed branch. 
That the appendicular organs, whatever they were (and every 
