497 
Origin of the U lodendroid Scar . 
diameter in the case cited ; this is considerably larger than the axis of any 
known lepidodendroid cone, and hence probably of any cone peduncle, 
which suggests that in some cases at any rate the lateral branches were not 
cones. 
The above brief discussion shows that halonial tubercles bore lateral 
branches (which may in some cases have been the peduncles of cones), 
which were shed by the intervention of an abscission layer, just as were the 
branches borne by ulodendroid scars, and that the two cases differ in 
the arrangement of the branches, in their position on the plant, and in the 
structure of the scars owing to the presence in Halonia of an aureola of 
leaf-bases pressed down by those of the branch, a condition only possible in 
Lepidophloios . 
Summary of New and Disputed Facts and Conclusions. 
i. In Lepidodendroids, small branches issuing laterally were sometimes 
shed by an abscission layer, developed from a cambium which forms across 
the base of the branch in all its living tissues, except that part of the primary 
outer cortex which lies outside the secondary cortex. This abscission layer 
becomes connected with the secondary cortex of the main stem, and in 
old age entirely takes on the structure of the latter. 
2,. The ulodendroid scar is such an abscission layer cutting off a branch 
which was formerly attached to its whole area. 
3. Halonia is essentially similar to Ulodendron , in that it represents 
a stem from which lateral branches have been cut off by an abscission 
layer. 
4. The most practical distinction between Halonia and Ulodendron 
lies in the arrangement of the branches, but the scars themselves are quite 
different when well preserved. 
5. The well-preserved halonial scar is divisible into two areas, of which 
the inner represents the abscission layer, whilst the outer results from the 
pressure of the long leaf-bases of the branch on those of the stem ; con- 
sequently the halonial condition can only occur in Lepidophloios . 
6. In some cases, at any rate, the lateral branch of Halonia was not 
the peduncle of a cone. 
7. No specimen of Ulodendron showing a well-preserved leaf-scar has 
ever been described, except in that type with oval scars and an eccentric 
umbilicus, which belongs to Bothrodendron . 
8. Consequently it is best to retain the generic name Ulodendron , as is 
done by most continental authorities. 
9. The reason why the leaf-scars are not found is that when whole 
branches were shed it was unnecessary to shed the individual leaves. 
