12 Hick, on Rachiopteris cylindrica, Will. 



the principal axis are accompanied by sections of struc- 

 tures that are almost certainty roots, and have some 

 resemblance to the organ in question. 



Division of the Axis. 



Looking at the whole series of sections with dividing 

 steles, it seems scarcely open to doubt that while in 

 equal division we have an indication of dichotomous 

 branching of the axis, in which the two members are 

 strictly homologous with each other and their common 

 podium, in unequal division of the stele we have an 

 indication of the formation of some lateral organ which 

 is not homologous with the axis from which it arises. 



As to the morphological nature of this lateral organ 

 or appendage, the evidence to hand is not sufficient to 

 justify any definite conclusion. The suggestion that it 

 is a foliar organ naturally and readily occurs, and that 

 may be its character. It would be in favour of this 

 view if the suspicion expressed above that the stele is not 

 radially symmetrical could be converted into certainty, 

 and this view is supported by the 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 peculiarities 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 hypothesis. In several of 

 his Memoirs* Williamson describes an unequal division 



*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. 



