324 Sampson. — The Morphology of 
this gap is closed, in this case by xylem, which appears between the edges 
of the gap and connects the stele with a single leaf-trace (sects. 3 and 4). 
It is this part of the stele which supplies the strand for the new tuber. The 
difference between the tuber strands, as they leave the stele in the two 
plants, depends partly on the fact that the tuber is far better developed in 
the one case than in the other. Whereas, in the plant with a single tuber, 
the stele divides almost equally, in the plant now under consideration only 
a relatively small mass of xylem passes out to the stunted tuber. A 
difference in form may also be noted, the stele of the stunted tuber being 
from the first a compact strand of xylem with a small core of enclosed 
parenchyma. 
The stele of one more fertile plant has yet to be described, since it is, 
perhaps, more typical of the smaller fertile plants in which the vascular 
tissue is less well developed. The plant in question possessed a cone, six 
leaves, and a somewhat slender new tuber. At the base of the peduncle 
two separate strands of xylem are found instead of a hollow cylinder as in 
larger plants. Lower down these increase in size, and a third strand 
appears, connected with a leaf-trace which joins the stele relatively early. 
The stele now shows a form roughly comparable with the horseshoe- 
shaped stele found at a corresponding level in larger plants, but it is less 
striking since the stele in the peduncle is already interrupted by large 
gaps. 1 In this plant no leaf-traces are connected with the vascular supply 
of the tuber. It arises from the medullated stele as a small arc of xylem, 
and, as it passes down the shaft of the tuber, it early becomes a slender 
cylindrical strand. 
In two of the three plants just described, a distinct break in the stele 
of the main axis was observed immediately above the point at which the 
strand of the new tuber is given off. Though less conspicuous in the 
smaller fertile plants, owing to the weaker development of the stele, this 
break was found in eleven of the twelve cases examined, while the one 
specimen in which a gap was not found showed a thinning of the xylem in 
a corresponding position. Although this gap generally extends for a very 
short distance, the sections in which it does occur present a most charac- 
teristic appearance, and one which has been noted by previous workers. 
Thus Wernham concludes that the ‘noticeable (J-form of the upper part of 
the stem is, perhaps, the most striking feature’, 2 while Jeffrey describes 
Phylloglossum as having ‘ a tubular stele, which, in the lower tuberous 
portion of the stem, constitutes in cross-section an almost continuous horse- 
shoe of xylem \ He states also that ‘the opening in the horseshoe corre- 
sponds to the outgoing strand, which passes into the resting tuber’. 3 
1 The stelar gaps of Phylloglossum are not regarded as foliar gaps,' though sometimes found in 
apparent connexion with leaf-traces (Jeffrey: Bot. Gaz., vol. xlvi, 1908, p. 245). 
2 Wernham : loc. cit., p. 33S. 3 Jeffrey : loc. cit. , p. 244. 
