ба пава. 
SPECIMENS OF 
LYGINODENDRON 
OLDHAMIUM. 355 
with one slight exception where the petiole fails to come off, but in ће branches 
this divergence is lost. 
It is unusual to find more than five distinct leaf- 
traces in the регісусіо of Lyginodendron*, but a primary branch in 
) E 
p = 
„— | 
. -J 
g 2, I3 
XLI 
12 
[E 
IO 
g 
8 
Tracings of outlines of nine successive 
sections of Dr. Scott's specimen, as 
shown by brackets on text-fig. 4. 
Horizontal shading = main axis; ver- 
tical shading = primary branch; 
black = leaf-bases. All reduced to 
three-fourths natural size. 
Dr. Scott’s specimen shows six, the phyl- 
2 
6 
(not 3), while a secondary appendage 
in the same specimen attains the number 
lotaxis being in two separate sets of 
of seven, where the divergence is pos- 
sibly #. The branches in the specimens 
overlap one another to some extent, so 
that it is quite usual to find. two branches 
in different stages of formation at the 
sime level. This probably has a good 
deal to do with the considerable disturb- 
ance of phyllotaxis. 
Unfortunately the preservation of both 
the specimens is too poor to allow of any 
detailed investigation of the behaviour of 
the vascular structures when a branch is 
given off. The secondary wood of the 
stem begins to swell below the point of 
exit of the branch. This swelling in- 
creases, so that usually quite a large bulk 
of secondary tissue 1s ready to pass out. 
Gradually separation of the two masses 
of wood takes place, and both parts close 
It is noticeable 
that there is frequently, if not usually, a 
up and are rounded off. 
good deal of secondary wood in the pith 
when a branch is being given off, and it 
seems possible that the anomalous tissue 
may help to close up the gap formed by 
the mass of xylem passing off to supply 
the shoot. 
A good deal of diversity exists in the 
manner in which the xylem of the branch 
behaves with regard to the petiole in 
whose ах] it is, as in some cases the 
petiole and braneh pass off quite independently, while in others they remain 
attached to one another until they have jointly separated from the stem, not 
parting company until a later stage. 
* Williamson, W. C., & Scott, D. H.: Phil. Trans. Roy. Soc. 1895 B, p. 709. 
