684 Browne . — Contributions to our Knowledge of the 
are situated at the periphery of the bundle and form bands or groups of 
elements, the long axis of each group pointing obliquely outwards. They 
develop some time after the carinal group, and the number of cells in each 
of these lateral strands varies according to the species from 3 to 15. Queva 
states that the lateral xylem is less developed in the rhizome and may even 
be absent there. According to him, too, the lateral metaxylem is composed 
entirely of spiral tracheides (Queva, p. 18); Eames, on the other hand, 
states that the elements of these lateral strands are in general scalariform, 
reticulate, or pitted, but that occasionally they contain annular or even 
spiral tracheides (Eames, p. 589). Bower (Bower (2), p. 389) quotes 
observations of Gwynne-Vaughan on E. giganteum , the details of which 
have not been published, but which were accessible to him ; according 
to these the lateral strands of this species contain 10-15 tracheides; the 
smallest of these are at the outside, and they gradually increase in size 
inwards. The larger elements are coarsely reticulate, the reticulation 
becoming finer and more regular in the smaller elements until in the 
smallest it closely resembles spiral thickening. 
Gwynne-Vaughan maintained, too, that the lateral metaxylem-strands 
show indications of centripetal development, especially in the larger species 
in which the lateral groups are better developed ; but he admits he was 
unable to prove this centripetal development as he had no incompletely 
developed portions of the stem (Gwynne-Vaughan). Bower endorses 
Gwynne-Vaughan s opinion with a similar reservation (Bower (2), p. 309). 
Queva, however, expressly states that the whole of the lateral metaxylem is 
centrifugal (Queva, pp. 25 and 35). Eames also regards the lateral xylem 
as centrifugal, though he records examples of a certain irregularity in the 
direction of lignification ; I have met with a few cases of similar irregularity 
in the fertile stem of E. arvense (Eames, pp. 591-3). My observations, 
which were not at all extensive, confirm Eames s view that the prevailing 
direction of lignification in the lateral strands is from within outwards, but 
that it is subject to occasional irregularities. In any case the lateral strands 
seem phylogenetically to represent centrifugal xylem. In the region of the 
annulus there is no reticulate nodal wood, and as we pass upwards towards 
the lowest whorl of sporangiophores the lateral groups of xylem become 
united by elements of a similar nature. Thus in the cone, both in the node 
and the internode, the xylem of the bundle consists not of three groups, but 
of a continuous band of tracheides. It seems very probable that in the 
vegetative internodes the lateral groups of xylem represent the free ends of 
a more deeply curved band of xylem. In that case the position of the 
tracheides of the lateral groups of metaxylem in a more or less radial series 
is due to the more or less marked curvature of a band of which only the 
carinal tracheides and the free ends are lignified. The primitive form 
of internodal bundle would then be that of the cone, an interpretation 
