ANATOMY OF CERTAIN SPECIES OF ENCEPHALARTOS. 457 



IS now at length yielding to, and has almost hccomc suppressed by, the modern and mon^ 

 efficient collateral type. In the later-formed vascular tissues of the axis, /. c, those in 

 regions other than the transitional one between stem and root, the collateral has entirely 

 superseded the concentric plan of structure, and as such is laid down from the earliest 

 stage onward all round the periphery of the central ring. 



With regard to the " accessory vascular strands " described by Scott as occurring in 

 the cortex outside the group of steles in the stem of Medullosa anglica, and figured in 

 plate 5, photograph 4, and in plate 12, fig. 18, of his paper, I fully incline to agree with 

 the author that they are probably " comparable to the cortical bundles of Cycas .... or 

 to the irregular strands which sometimes occur in the extrafascicular region of Wacro- 

 zamia.'' But I go further, and say that these accessory strands are homologous, not only 

 with those of Cycas and 3Iacrozamia mentioned, but, I would add, with those of 

 Encephalartos horridus, Lehm., as seen in fig. 9, and therefore, according to my own 

 view, with the successive vascular rings in the stem of Cycas, Macro::amia, Encephalartos, 

 and the MeduUosese. It is exceedingly interesting to note that these "accessory strands " 

 contain in their central parenchymatous portion the same short reticulate tracheides 

 as I have described for the vascular strands of Cycas, EncepJialartos, and ITacrozamia. 

 This is a point of much importance. Scott says : — '* We know .... that some 

 MeduUoseae (e. g. M. stellata, var. gigantea) formed successive extrafascicular zones of 

 wood and bast outside their stelar system, just as we find in Cycas, Macrozamia, and 

 Ihce'phalartos at the present day. It is therefore not surprising that in our species we 

 should meet with other characteristic Cycadean anomalies." Little wonder, indeed, if, as 

 I believe, these " other anomalies " are entirely homologous with the former ones. The 

 author says further : — " The accessory strands in M. anglica are certainly quite different 

 from the normal steles and leaf-traces ; neither can they be identified with the strands 

 supplying adventitious roots, which had a more horizontal course. There is no indication 

 of their connection with any other form of lateral appendage." All quite true. But the 

 explanation which I have given of these structures, especially after comparing them with 

 the cortical vascular strands of Tlnceplmlartos horridus^ Lehm., exhibited in fig. 9, will 

 alone avail to save the unsatisfactory process of relegating these '* accessory strands " to 

 the category of undefined " anomalous " structures. 



The term "anomalous" I hold, moreover, to be inappropriate, as applied to the 

 " extrafascicular " rings of vascular tissue in the three genera of Cycads and certain 

 species of Medullosa, for it implies that these structures cannot be classified and defined 

 like the other structures of the order, a supposition which, as I have above tried to show, 

 is false. I hold that there is nothing "anomalous" in these strands, but that they 

 constitute part of the morphologically-inherent structure which has for long ages been 

 characteristic of the group in which they are found. They are thus fundamentally 

 different in nature from the structures, more or less similar in appearance, occurring in 

 the stem and root respectively of such plants as Tecoriia and Beta, which are purely 

 adaptive in character, L e., have been specially adopted, within a comparatively recent 

 period, to suit the special physiological necessities of the plants in wluch they occur. 



