29 
Anatomy of the Ophioglossaceae . III. 
a little higher up, before any indication of the departure of the first leaf- 
trace was evident. Longitudinal sections of this region in other plants 
showed that the central xylem consisted of spirally thickened tracheides, 
while the peripheral ones were pitted. Owing to this structure, the stele 
was described in my earlier accounts as centrarch, the inner xylem being 
regarded as protoxylem, which it resembles histologically. For reasons 
that will be further evident below, I am now led to distinguish even in these 
slender steles between inner and outer xylem, as in the case of the branches 
previously described, and to correct in this sense my earlier statements. 
Text-fig. 7. Series of transverse sections of the rhizome of a small plant, developed from an 
embryo, to show the relative positions of the various organs. The outline of the rhizome is given, 
that of the stele is a dotted line, the xylem is black. Description in text. Z. 1 , I. 2 , Z. 3 , Z. 4 , Z. s , succes¬ 
sive leaves or leaf-traces ; r. 1 , r 2 , r. 8 , r 4 , r. 5 , successive roots; vb. 2 , second vestigial bud. The slits 
leading to other vestigial buds are also shown. 
The stelar xylem in the hypocotyl can be regarded, as in the further 
regions of the shoot, as composed of a dorsal portion destined to continue 
outwards as the first leaf-trace, and a ventral portion which is more strictly 
cauline. At the level of the section represented in PI. 3, Photo 41, the arc 
of outer xylem destined for the leaf-trace is rendered distinct from the 
lower portion of the stele by the group of parenchyma immediately within 
its endarch protoxylem. The true protoxylem for the trace was evidently 
placed immediately within the outer xylem, thus indicating the mesarch 
