146 
DR JOHN M‘LEAN THOMPSON ON 
shown in the stem beneath the point of separation of leaf-sheath and axis. In this 
case, as in Stromatopteris , the assumption of an erect position by the leaf, and the 
accompanying lateral displacement of the flower-bearing axis, are linked with a con- 
tinuation of the structural features of the axis into the leaf itself. 
The second specimen of Stromatopteris may now be briefly described (fig. 4l). 
Its slender axis is incomplete below, and near its base it is branched. The right 
branch has been broken off, but the left is continued obliquely upwards for a short 
distance. It is then sharply diverted from the oblique position to the vertical, and 
is finally branched. The right member of this branching has also been broken off, 
and the left limb is continued vertically upwards for a considerable distance before, 
finally dividing. The basal portion of the right branch thus formed is little more 
than a nodular swelling, while the remainder is a slender tapering column, ending 
above in a small rounded tip. The left-hand limb is slender, and, while its linear 
form is maintained throughout, it bears at about one inch from its base a small 
incomplete horizontal branch. The general position and the smoothness of surface 
of the two distal branches suggest that they are of petiolar nature, while the rugged 
appearance of the remainder of the specimen confirms the latter as axial. 
The anatomy of this specimen is of special interest as confirming the opinions 
expressed regarding the first specimen, and supplying a demonstration of the 
complete local abortion of axis which the first plant prefigured. The basal sections 
of the .stem show a simple protostele (fig. 21), and, as the point of first branching 
is approached, a widening and equal division of the stele occur (figs. 22 and 23). 
The broken branch is supplied by the right protostele, while the obliquely 
ascending limb receives the left (fig. 24). The latter stele quickly widens (fig. 25), 
and divides into two unequal protosteles, the smaller of which is directed towards 
the left or convex surface of the oblique axis (fig. 26). These two protosteles become 
widely separated, though still completely enclosed by the cortex of the stem, and as 
the widening increases the left-hand stele dwindles rapidly (fig. 27). Beneath the 
point where the left surface of the stem is sharply changed from a convexity to a 
concavity, this smaller stele suddenly dies out, while the remaining protostele passes 
on into the erect continuation of the axis (fig. 28). The sudden change from the 
obliquely ascending to the erect position of the axis has accordingly found its 
explanation. The stele has been branched preparatory to a forking of the axis, but 
one limb of this forking has been suppressed, and the point of change from convexity 
to concavity marks the position of the arrested branch. It has been noted that in 
the first specimen of Stromatopteris arrest of axis was confined to the distal leaf- 
bearing branches, but in the second specimen abortion has been continued downwards 
into the lower branches. There will then be little cause for surprise when it is 
found that reduction and abortion are even more prominent in the distal portions of 
this specimen than they were in the corresponding parts of the first plant. 
The steps of stelar division which precede the next branching are represented in 
