BRANCH OF LEPIDOPHLOIOS FULIGINOSUS. 227 
degeneration, would not be of much value. In one portion of the section the large 
spaces are absent, and one can see, though somewhat indistinctly, that their place is taken 
by a small-celled tissue, which is, however, not well preserved (Pl. 26. fig. 9, ph.), and with 
a high power it can be seen that most of the cell-walls are broken. It is interesting, 
however, to note that the small-celled groups corresponding to the spaces in other parts 
of the section are lighter in appearance than the intervening tissue, which is not 
generally the condition of secreting tissues. 
In longitudinal section it will be seen from PI. 23. fig. 8 that even where the large 
spaces have made their appearance by absorption of some of the cellular tissue, the 
transverse walls are still in part preserved, and show that the groups of cells were 
arranged in vertical series separated by transverse walls following each other at no very 
considerable distance. 
The phloem does not form a continuous cylinder around the stem, but is broken 
up into numerous pieces by the leaf-trace bundles which pass out through the phloem 
into the cortex. This is shown in fig. 7, Pl. 24, and is also represented in the drawing, 
Pl. 25. fig. 13. Here it will be seen that, in passing out through the phloem, the 
vascular leaf-trace becomes associated with a group of phloem elements which accompany 
it to the outside of the stem. This e ak: gets rather darker, being composed ` 
of smaller and more closely-set cells. 
As will be seen in Pl. 24. figs. 7 & 12, the tissue immediately outside the phloem has 
been split during mineralization almost along its whole extent. This is no doubt due to 
the very delicate character of its cells, which are thin-walled and rectangular, and 
from the regular sequence of their walls appear to be of a meristematic nature. As will 
be seen from Pl. 25. fig. 19, which shows an enlarged view of this region, there are never 
many of these thin-walled cells, but generally only two or three. Such a meristem 
I have observed in other specimens of Lepidophloios fuliginosus. 
A tissue of very similar appearance, but belonging to the middle cortex, is found in 
the stems of Lepidodendron vasculare (Binney), and is well figured by Scott (1900) *. 
In my specimen, however, this meristematic zone lies within the inner cortex, and 
would be morphologically identical with the pericycle,in which the appearance of 
meristematic cells would not be surprising. This outer meristematic layer I would 
| compare with the meristematie zone in the pericycle of certain monocotyledons, and it 
could also be compared with the meristem retained in Zsoéfes, for, according to Scott and 
Hill (1900), the first normal cambium on the inner side of the phloem disappears at an 
early period in Zsoétes Hystrix, and is followed by a second eambium which soon arises 
further to the exterior. It is of interest, with regard to the systematic position of 
Isoëtes, to find in the Lepidodendracee so distinct a secondary meristem outside the 
phloem. 
Whether any addition to the phloem region is made from the pericyclic meristem, it 
was not possible to definitely ascertain in these sections, but in one or two places the 
arrangement of the outer phloem elements suggested such an origin. 
* Scott, D. H. (1900), fig. 54, p. 134. 
