3 28 
Sampson . — The Morphology of 
completely disappears. This apparent disintegration and dying out of the 
upper part of the stele in sterile plants is the most striking feature in their 
anatomy, and one demanding an explanation. Earlier in this paper 
(p. 321) a plant was described in which the stele of a storage tuber made 
a sharp upward bend as it passed out, and this bend was taken as indicating 
a change in direction of growth. It may be noted that sections through 
this bend correspond very closely with transverse sections taken at a certain 
level in sterile plants, and the apparent dying out of the upper part of the 
stele in these plants may be due to a sharp bend in the axis. If this be so, 
sterile plants must consist of a slender unbranched axis, which bends over 
and forms the annual storage tuber. In support of this is the fact that 
Professor Bower, working on the ontogeny of the yearly growth of sterile 
tubers, identified the growing point of the new tuber with the apex of the 
stem itself. 1 
In the largest sterile plant examined, the course of the stele is some- 
what different from that described above, the chief difference being that it 
is for a short distance medullated, as are the steles of fertile plants, and the 
tuber strand, as it passes out, assumes the characteristic U-form. More- 
over, the medullated stele shows a break which, corresponding in position 
to the tuber stele, recalls the ramular gap of fertile plants. The upper part 
of the stele is, however, apparently lost among the leaf-traces as in other 
sterile plants. 
The U-form of the tuber stele, and the break which occurs in the stem 
stele above the level of its exit, are difficult to bring into line with the con- 
ception of sterile plants suggested above. They are explained, however, 
if, on analogy with fertile plants, it be assumed that branching has occurred 
on the formation of the new tuber, but that here the fertile branch has been 
arrested early in its development. It seems probable, therefore, that two 
conditions may exist in sterile plants : that a sterile plant may consist 
either of a simple axis, concerned only with the formation of a storage 
organ, or of an axis which has divided, one branch forming a tuber, the 
other being completely abortive, thus representing a condition intermediate 
between the small sterile and the simple 2 fertile plants. In either case the 
anatomy of sterile plants bears out the conclusion that the tuber of Phyllo- 
glossum is the specialized terminal part of a leafy axis. 
VI. Branching in Phylloglossum. 
Phylloglossinn has hitherto been regarded as a typically unbranched 
form of Lycopod, the rare cases of branching which have been recorded 
being restricted to the cone-bearing axis. Professor Thomas states that 
1 Bower : loc. cit., 1886. 
2 ‘ Simple ’ here refers to fertile plants with a single new tuber in which the axis is, therefore, 
only once branched. 
