1042 
de Fraine. — On the Slruchtre and 
bundles either radially symmetric or unilateral in type. It could not be 
determined whether the radially symmetric foliar strands ever divided 
further to produce the smaller unilateral traces. Unfortunately neither 
Scott’s fossil nor the new stem enables the question to be definitely settled 
as to whether the whole vascular mass which separates from the main stele 
is completely used up in the production of leaf-traces, but the great proba- 
bility that they were has already been shown by a comparison of the 
behaviour of the ‘ meristeles ’ a 1 , y 1 , and y 3 . 
The very interesting cases recorded by Scott of the ‘occurrence of 
fusion between meristeles probably of quite distinct origin ’ do not occur in 
the new stem, though instances of re-fusion of ‘ meristeles’ of similar origin, 
and of a ‘meristele’ with the main stele, have been already described. The 
distribution of the ‘meristeles’ around the central strand appears to be 
in the form of parallel cords of vascular tissue rather than in the state 
of ‘ a kind of network round the stele ’ ; 1 the network in the new stem 
is provided by the extrafascicular arcs which will be described later (com- 
pare Text-figs. 4 and 5). One further question still remains to be con- 
sidered. Are the ‘ meristeles ’ to be considered as a leaf-trace system, 
or are they to be considered as part of the stelar system proper to the 
stem ? In discussing this question Scott points out the marked agreement 
between the meristeles of Sutcliffia insignis and the large concentric strands 
which leave the stele in Medullosa anglica ; in both there is the same close 
agreement between the steles and the large strands given off from them. In 
M. anglica these main foliar strands, which are concentric at first, break 
up entirely into collateral bundles which enter the bases of the leaves, that 
is, they represent a leaf-trace system only. Scott concludes that they cannot 
c be directly compared to the meristeles of Sutcliffia ’ because in Medullosa 
anglica ‘ there is no evidence of fusion with neighbouring strands, nor any 
indication that part of the strand remained behind in the stem after the 
foliar bundles were given off’, and for these reasons he interprets the vascular 
structure in Sutcliffia as a protostele giving off a peripheral system of sub- 
sidiary steles which form the points of departure of the actual leaf-traces. 
The discovery of a portion of a second stem tends to show, though the 
evidence is unfortunately not absolutely complete, that the meristeles were 
completely used up in the formation of leaf-traces ; in all probability none 
were left behind exclusively cauline in nature ; further, fusion of neighbour- 
ing strands was not of common occurrence, and may have been merely 
a consequence of the crowding together of numerous ‘ meristeles \ In 
connexion with this point, moreover, it must be remembered that fusion of 
leaf-trace bundles is a not uncommon occurrence in the Medulloseae. The 
‘ meristeles ’ of our stem appear to offer a close comparison with the leaf- 
trace strands which leave the stele in Medullosa anglica ; in both a large 
1 Scott : loc. cit., p. 53. 
