Relation of Pt endosperm Anatomy to that of Cycads. 5 t 
parenchymatous in nature, its texture being similar to that of the 
Cycads. The main differences from Heterangium consist in the 
presence of large accessory vascular strands (“ meristeles ”) round 
the stele of the stem, and in the more complex vascular system of 
the petioles. The meristeles separate from the main stele, and are 
at first concentric in structure, being surrounded by secondary 
tissues. They divide repeatedly, forming either unilateral or radially 
symmetrical concentric foliar traces. The ultimate traces have no 
secondary tissue, this having been gradually lost. In Miss de Fraine’s 
new specimen extrafascicular bands of wood and phloem, showing 
occasional inverse orientation, form a network round the stele and 
the leaf-strands. The vascular strands of the petioles belonging to 
Sutcliffia are concentric as in Heterangium, but they are numerous 
in each petiole, as in recent Cycads. The whole leaf-supply system 
is thus much more complicated than in Heterangium. 
The evolutionary tendencies of the Medullosean alliance, like 
those of the Lyginopteridean group, seem to have found expression 
in progressive complication of the vascular system, for in all types 
except Sutcliffia, polystely prevails. 
Medullosa anglica (11 ; 14, p. 428) represents so far as is at 
present known, the next stage to Sutcliffia in vascular evolution. 
It, also, is of Lower Coal Measure age. The stem, instead of being 
monostelic as in Sutcliffia, possesses three equivalent steles, each 
one having the same structure as the single stele of Sutcliffia, except 
that the protoxyiems are mesarch (Fig. 7). A stele of Medullosa 
anglica is thus better compared with the stele of Heterangium. In 
sf 
Fig. 7. —Medullosa anglica. Transverse section of stem, showing three large 
leaf-bases, a, b, and c. ab, be, position of next leaf-bases above, st, the three 
steles ; It, leaf-traces ; an, accessory rings of wood and bast; pd, periderm 
forming a ring round the group of steles, and also enclosing one of the accessory 
strands; r, adventitious root; oc, hypoderma; sc, sclerenchymatous band 
between leaf-base and stem. (After Scott, 1899). 
