FROM THE LOWER COAL-MEASURES. 53 
between meristeles probably of quite distinct origin, as shown clearly in the second 
case (B) and indicated in « also. The occurrence of fusion suggests that the meristeles 
may have formed a kind of network round the stele, new meristeles springing at 
intervals from the latter, to compensate for those parts of the reticulum which were 
used up in the formation of leaf-trace strands. 
The origin of the latter is not completely cleared up by the two cases investigated, for 
we have not been able to trace the strands given off from the meristeles to the stage 
where they become typical foliar bundles. Probably the length of stem covered by the 
17 transverse sections is not enough for this. 
Hence it is desirable to begin with a meristele already free from the stele, and trace 
it through the upper part of its course. 
As our example, we may choose a small meristele (m.) lying just off the promontory 
we have called « (figs. 1 & 7), with which, however, it probably had no connection. 
At the bottom of the series this meristele (itself no doubt the product of the previous 
subdivision of some larger mass) measures about 3x2 mm. It shows distinct traces of 
secondary wood, absent only on the side towards the stele. There is a small bundle to 
the left, which has probably been derived at a lower level from this meristele. Up to 
Section IV. the meristele remains unchanged except for some rearrangement of its 
elements. Fig. 7 (Pl 8) shows it as it appears in Section III. In Section V. the 
meristele has broken up into three bundles (m.d.), each a little over 1 mm. in diameter - 
(Pl. 7. fig. 2) and of similar structure to that represented in fig. 14 (Pl. 9). The three 
bundles are shown at a somewhat higher level (Section VIIL) in fig. 8 (Pl. 8); 
here the innermost of the three remains near its original position, while the other 
two, accompanied by the one that became free previously, have moved towards the 
outside. In succeeding sections these three bundles travel further and take their 
places in the peripheral rank of leaf-traces. The inner bundle remains behind, and no 
doubt simply forms one of the internal strands of the cortex or leaf-base (Pl. 7. fig. 5, 
Section X.). : 
This completes the history of the course of the bundles in the stem ; the meristele 
from which we started is of similar dimensions to some of those of which we have traced 
the origin in the previous series z and 6. Hence if we combine our new data with those 
derived from one or other of these series, we have the complete course of the vascular 
strands, beginniug with the first separation of the main meristeles from the stele, 
proceeding through their various subdivisions, and ending with definitive foliar bundles 
belonging to the leaf-base. iude 
It may be mentioned that the bundles in the leaf-bases frequently fuse and branch. 
An example of a fusion between two of these strands is shown in PI. 7. fig. 5, moo. * 
The question remains: Are we to regard the whole as a. leaf-trace system, or should 
considered as a part of the stelar system? In other 
the main meristeles rather be à TA 24 
words, are the meristeles to be compared with the large leaf-traces given off amm wate 
steles in Medullosa anglica, or with the steles themselves P e de ee ~ 
In that plant the leaf-trace, where it first becomes free from the stele, isa large, atin * 
concentric, strand, with primary wood from ‘5 mm. to 1 mm. iu diameter, v stru ure 
SECOND SERIES.—BOTANY, VOL. VII. 2 p 
r4 
