Affinities of Sutcliffia. 1055 
strands is the extraordinarily close parallel they afford with the successive 
vascular rings characteristic of certain genera of the Cycads, namely, Cycas, 
Encephalartos , Macrozamia , and Bowenia . Not only is the arrangement of 
the secondary strands in arcs, fan-shaped masses, and occasionally concen- 
tric bundles closely similar in Sutcliffia and in the above-mentioned genera 
of the Cycads, but comparison with the descriptions and figures given 
by Worsdell 1 in his series of papers on Cycadean anatomy shows that the 
intimate structure is practically identical also. Large isodiametric tracheides 
occur at the edge of the wood in both cases, the great development of 
the medullary rays results in a very parenchymatous xylem in both living 
and fossil stems, while in both occasional inversion of the strands is found. 
One further point still remains to be considered, namely, the origin of 
the extrafascicular strands of the Cycads. Worsdell (loc. cit., 1900, p. 452) 
considers the large, irregularly-shaped, reticulately thickened tracheides of 
the extrafascicular rings are homologous with the reticulate tracheides of 
the central region of the cortical concentric strands of the stem and leaf 
of Cycas, and in this genus he was able to observe their development. In 
Cycas revoluta , Thunb., he found ‘ the first-formed vascular elements arose 
by tangential division of the large, rounded or angular, cortical or pericyclic 
cells resulting in the large, isodiametric, irregularly-shaped tracheides of 
precisely similar shape to those cells. After one or more such elements 
have been cut off, the parenchyma cells begin to divide radially as well as 
tangentially, in this way forming smaller and smaller elements with each 
centrifugal division, until at length the majority of the tracheides are of the 
same size and shape as those of the central cylinder or stele.’ The dis- 
placement of the large first-formed tracheides by pressure of surrounding 
tissues, and the great difference in size between them and the later-formed 
ones, render ‘ the determination of their mode of origin, at an older stage of 
the same vascular tissues, utterly obscure. The similar reticulate tracheides . 
in the cortical concentric strands ... in all probability arise in precisely the 
same way.’ [It is of interest to note that in an isolated, concentric strand in the 
cortex of the upper regions of the hypocotyl of one seedling of Macrozamia 
spiralis , 2 the central core of the bundle consisted of short tracheides which 
were surrounded by a zone of cambium and cambiform cells, the few im- 
mature xylem-elements present were developed centrifu gaily from the centre 
of the bundle.] Quotation at length has been made from Worsdell’s paper 
1 Worsdell, W. C. : I. The Anatomy of the Stem of Macrozamia compared with that of other 
Genera of Cycadeae. Ann. of Bot., vol. x, 1896. II. The Comparative Anatomy of Certain Genera 
of the Cycadaceae. Journ. Linn. Soc., vol. xxxiii, 1898. III. The Comparative Anatomy of 
Certain Species of Eniephalartos. Trans. Linn. Soc., Oct., 1900. IV. Contributions to the Com- 
parative Anatomy of the Cycadaceae. Trans. Linn. Soc., Sept., 1901. V, The Structure and 
Origin of the Cycadaceae. Ann. of Bot., vol. xx, April, 1906. 
2 Hill, T. G., and de Fraine, E. : On the Seedling Structure of Gymnosperms. III. Ann. of 
Bot., vol. xxii, 1909, p. 442. 
