the Anatomy of the Cone and Fertile Stem of Equisetum . 441 
the uppermost whorl of leaves and the basal whorl of the cone alike consist 
of five members. This failure to form a closed ring of xylem at the last node 
of the branch is clearly due to vascular reduction, not a surprising con- 
clusion when we remember how reduced a vascular system is the network of 
strands constituting the stele of the cone of this species. 
In Cone E the annulus, as seen in transverse sections of the axis, 
showed four very small groups of 2-4 tracheides running obliquely, but 
nearly horizontally, upwards through its parenchyma. None of these 
tracheides was in connexion with the tracheides of the axis, nor were the 
narrow, parenchymatous, phloem-like and endodermis-like cells that accom- 
panied them and had a like orientation with them in connexion with 
the corresponding elements of the axial stele (PI. XXI, Fig. 3). The latter 
type of cell, however, approached closer to the stele than the tracheides. As 
the limits of the annulus and axis are not sharply defined, it is difficult 
to say how far, if at all, the annular bundles penetrate the axial parenchyma. 
As Miss Barratt has shown that the first tracheides of the leaf- trace to be 
differentiated are situated distally, and that lignification proceeds in the 
direction of the axis (Barratt, p. 207), it might be thought that, in view of 
the immaturity of Cone E, these small annular bundles would later have 
become connected with the stele of the axis. But, apart from the fact that 
the specimen is not young enough to show so incomplete a stage of de- 
velopment, the inner termination of the annular tracheides was usually 
marked by the presence of endodermis-like cells, cutting the annular 
tracheides off from the axial stele. In the reconstruction (Text-fig. 7) these 
small free, annular bundles (cf. Browne ( 3 ), p. 254) are shown as small crosses, 
white on black and black on white, on the strands and meshes at the level 
and on the radius of their dying out. 1 
Miss Barratt states that though the vascular structure does not support 
the view that the annulus is of foliar nature it cannot be said to throw much 
light on the morphology of that organ. The arguments she gives against 
the foliar nature of the annulus are, firstly, the course of the protoxylem 
strands in the region of its insertion, and secondly, the total absence from it . 
of vascular supply. The latter argument she admits not to be an insuper- 
able objection to the foliar theory, ‘ because the ochreola which occurs 
at the base of all branches always lacks traces * (Barratt, p. 228). As 
a matter of fact the ochreola is not always completely devoid of vascular 
elements, 2 but, since it is usually devoid of vascular supply, the absence of 
traces from the annulus is, as Barratt recognizes, no insuperable objection to 
its being regarded as a reduced leaf-sheath. Moreover, in two cones of 
1 The white cross, which should be shown on the first strand of Text-fig. 7, is unfortunately 
almost undistinguishable. 
2 Milde in 1867 recorded the occurrence of a few tracheides in the ochreola of E. arvense and 
E. limosum (pp. 157 and 346, PL II, Fig. 36), while in 1876 Janczewski indicated, in a reconstruction 
of a node, the presence of vascular tissue in the ochreola of E . arvense (Janczewski, PI. II, Fig. 9). 
