576 Hatfield ’ — Anatomy of the Seedling and 
outer boundary of the vascular ring. This structure suggests in some of its 
features that found by Dr. Stopes 1 in the stem of the cretaceous fossil 
Colymbites Edwardsii. The wood of Colymbites is a single vascular 
cylinder, composed of alternating bands of radial and tangential xylem 
elements, and it seems likely that this whole structure is the product of one 
cambium. It is of interest to find, in a living Cycad, a vascular cylinder 
which shows a similar alternation of a radial and a tangentially elongated 
band of wood, and which is therefore in some degree comparable with that 
remarkable fossil. 
In the living plant this arrangement extends to the phloem also, which | 
was not preserved in the fossil (Plate XXII, Fig. III). 
It is unfortunate that these plants were fixed very roughly, and that 
the cambial tissue is somewhat collapsed in all specimens. Nevertheless, 
it seems quite certain that the cambium cells were themselves tangentially 
extended, and, indeed, the whole phenomenon is probably the result of this 
stretching of the cambium. The causes which may have led to this will be 
discussed later. 
(6) The anomalous ring. Soon after the establishment of tangentially 
running elements in the xylem and phloem of the vascular cylinder, patches 
of meristematic cells are observed in the starchy tissue which lies between 
the peripheral lignified fibres of the vascular cylinder and the inner cortical 
region of starch-depleted tissue referred to above. The initiation of this 
secondary cambium seems to bear some relation to the stretching phe- 
nomenon just described. Tangentially running elements do not appear 
simultaneously at all points of the stem ; there may be a considerable 
development of those elongated tracheides at one or two points of the 
circle, whereas at other points normal radial elements are still being formed. 
In such cases the abnormal cambium seems to arise first outside those 
areas of the vascular cylinder which have undergone tangential extension. 
It is suggested that the two phenomena may be due to some common 
cause. Within this abnormal cambium, and probably formed by it, groups 
of extremely irregular lignified ‘ transfusion 5 elements are observed, recalling 
the tracheides found on the internal faces of anomalous rings in the mature 
stem of this species. 2 In that region of the stem where the first anomalous 
cambium is well established and is becoming functional, there are very 
obvious patches of conducting elements, forming an integral part of the 
anomalous ring (Plate XXII, Fig. Ill), but which would appear to be de- 
veloped in connexion with the outgoing leaf-traces. At this stage the strand 
itself cannot usually be followed far into the cortex, and may often seem to 
end in the anomalous ring, thus giving rise to the appearance of special 
£ anastomoses ’ between the two systems. Whether anastomoses may occur 
1 Stopes: Catalogue of the Cretaceous Flora, Part II, p. 314 et seq. 
2 Worsdell : loc. cit. 
