TURCUCETMOEN  GUME wa, a "NEN Sn SO eee ke ue i 
88 DR. D. H. SCOTT ON THE HETERANGIUMS 
but died out, and the structure is that of an ordinary stem of tbe a form. 
The branch is very similar to the smaller stem (24) appearing in the same 
section, and it is quite likely that the latter may represent another branch of 
the same main axis. It is evident that secondary growth started at the base 
of the branch, where it also slightly affected the parent stem. 
As regards the nature of the æ form of stem, there is no doubt that it has a 
distinetive anatomical habit, and we cannot wonder that Williamson at first 
inclined to make it a separate species. Even allowing for the better 
preservation of the cortex in the younger stems, the difference can hardly 
be reduced to one of age; I have seen no B stems that can naturally be 
interpreted as the older stages of æ stems. The youngest 8 specimens, which 
ought to come nearest to the « form, do not possess the powerfully constructed 
cortex which characterizes the latter. 
Not much stress can be laid on the fact that an «æ specimen is the only one 
that shows branching. ‘The specimens after all are few, and we must 
remember that it was a long time before branching stems of Lyginopteris 
oldhamia were found, common as the plant is. In ZJeterangium generally, 
branching must have been extremely rare ; whether it was soin the Dulesgate 
species we cannot tell. 
The various forms of stem described under H. Lomaaii all occur in a single 
coal-ball ; it appears that none of them have been found in any other block. 
It seems almost infinitely improbable that two or more distinct species of the 
same genus, each of the extremest rarity, should happen to be associated in 
one unique nodule; the presumption is overpoweringly strong that all the 
specimens belong to one and the same species. The æ form is the most 
distinet in appearance, but I do not doubt. that Williamson's later view was 
essentially correct and that it represents a younger stage of growth of one 
of the other Dulesgate forms of stem, though not perhaps of a form exsetly 
identical with any of those which we possess in a more advanced state. 
Whether the differences among the specimens of H. Lomawiti are due to 
variability in homologous stems, or to the occurrence of multiform stems in 
the same plant, cannot be decided. The latter seems more probable, but we 
have no proof, for in the only case where a stem has been observed to branch 
the branch merely repeats the characters of the parent axis. 
Petioles. 
The evidence we have collected so far only proves that in H. Lomazii 
two bundles, each showing signs of division, entered the leaf-base ; we do 
not yet know how many distinct strands were present in the petiole. The 
material contains a few specimens of petioles, though none are well preserved. 
As they are associated with various forms of H. Lomaaii stem, it is impossible 
to tell to what particular form they belonged ; from their size, they were pro- 
bably borne on the larger stems. Three of these petioles are tolerably clear—a 
section of one of them is shown in Pl. 4. fig. 18. In other sections of the same 
