64 THOMAS HICK, B.A., B.SC, A L.S. 



negative evidence that besides the appendages in question, there is 

 nothing else that can be regarded as suggestive of leaves ; indeed the 

 absence of anything like an ordinary leaf-trace bundle, both in the 

 cortex and at the periphery of the xylem, is one of the pecularities of 

 this plant. But of positive evidence, as just stated, there is not 

 nearly enough to justify a conclusion. 



On the other hand, the large size of the detached portion, relatively 

 to that of the whole stele, is hardly in accordance with the foliar hypo- 

 thesis. In several of his Memoirs 1 Williamson describes an unequal 

 division of the stele of Lepidodendron, which in some respects resembles 

 that met with in our plant. But in these cases it would seem that the 

 detached smaller segment soon becomes changed into a radially 

 symmetrical stele, similar, in essential points, to that from which it 

 originates, a condition of things which has not been found in Rachiop- 

 teris cylindrica. According to Williamson, this mode of branching in 

 Lepidodendron is associated with the formation of fruit-spikes or 

 strobili, into the axes of which the branches of the stele, successively 

 formed by unequal division, are distributed. While there is a 

 possibility, then, that in our plant the lateral appendage may be some 

 form of fruit or an organ axial in its nature, the character of its stele 

 is rather opposed to such an interpretation than in favour of it. 



Fig. 6, which is taken from No. 102, shows what are probably the 

 relations in space between the axis and its offshoots. At A and B we 

 have two normal axes which have apparently arisen by the dichotomy 

 of a common podium. Just below A is a section, a, of what appears to 

 be a root, while another, r, is seen just above B. Below B, at s, is one 

 of the unknown lateral appendages. Symmetry of arrangement would 

 suggest a lateral appendage above A, but the periphery of the latter is 

 at the extreme edge of the preparation, and it is impossible to say 

 whether such an appendage was or was not originally present. The 

 stele of B is undergoing unequal division in a plane at right angles to 

 that which contains all the other sections. 



What is Rachiopteris cylindrica ? 

 Whatever mterest or importance may attach to the anatomical 

 details set forth in the preceding pages, it must be admitted that they 



1 See Part II. Phil. Trans., 1872; Part XI. Phil. Trans., 1881 ; Part XII. 

 Phil. Trans., 1883; Part XVI. Phil. Trans., 1889; and Part XIX. 

 Phil. Trans., 1893. 



