253 
Medullosa from the Lower Coal Measures. 
nature of the fibrous groups, the strands of parenchyma cells being larger 
in the hypoderma (hy.) than in the limiting band (sc.b.), and also in the fact 
that secretory canals are abundant in the hypodermal region, but are almost 
entirely absent in the limiting zone. In the sections 8 and 9, cut from 
portion 2 of the coal-ball, the limiting zone sc.b. is present only in the form 
of a band of sclerenchyma precisely similar to sc . 1 or sc. 2 . The passage 
from the simple sclerenchymatous band to the more complex limiting layer 
sc.b. could not unfortunately be traced, since it lay between sections F 
and 8. There can be no doubt, however, that in the lower parts of the 
adherent leaf-base its tissues are separated from those of the stem by 
a continuous sclerenchymatous layer; this layer became broken up into 
strands of fibres by the ‘ intrusion ’ of parenchyma tissue as the nodal region 
above was approached, and finally, by the increase in the parenchyma and 
the association of secretory canals, the limiting layer approximated to the 
hypoderma of the leaf-base, with which it became continuous as the petiole 
separated from the stem-tissue at the node. 
The hypodermal layer is of the form described by Renault as the 
Landriotii type, 1 and the leaf-base as a whole shows a characteristic 
Myeloxylon 2 structure. 
Lying between these two leaf-bases lb 1 and lb . 2 are two much less 
prominent tissue masses, at either end of the short diameter of the stem ; 
they are labelled lb? and lb? respectively. Their structure repeats on 
a smaller scale that of lb . 1 and lb 2 : a band of sclerenchyma (.sr. 3 ) occurs 
in the upper sections of the series, cutting off part of the leaf-base lb? ; in 
the lower sections this band cannot be made out. It is possible, of course, 
that the regions marked lb? and lb? represent the true cortical tissues 
of the stem, but the presence of the band sc? in the upper part of the 
series, a band which appears to be characteristic of an adherent leaf-base at 
its lower end, would appear to render the view that they represent the 
extreme bases of leaves the more tenable one. 
If this view be maintained, then the specimen represents a portion of 
a stem entirely surrounded by four spirally arranged adherent leaf-bases. 
No petiole becomes free from the stem during the course of the series, but 
a consideration of the nature of the ‘ limiting layer ’ (sc. 1 , sc. 2 , sc?, and 
sc.b., Text-fig. 1) during the series shows that the leaves left the stem in 
the order lb. 1 , lb?, lb?, and lb?. Of these, lb 1 represents the oldest leaf- 
base ; it probably separated from the stem at a distance not very much 
above the level of the top section. The leaf-bases were decurrent down 
the stem for a considerable distance (for at least four internodes), so that in 
life the stem with its distant nodes presented a ribbed or winged appearance. 
1 Scott, D. H. : Studies in Fossil Botany, 2nd ed., Pt. II, p. 445. 
2 Seward, A. C. : On the Genus Myeloxylon (Brong.) Ann. of Bot., vol. vii, p. 1, March, 
1893. 
