6 LANG, Morphology of the Stock of Isoetes Incus tris. 



Stokey, 6 in a paper mainly concerned with the histology 

 of the secondary tissues, suggested that the tuberous 

 stock of Isoetes " is not wholly stem, but a contracted 

 stem and main root" She does not, however, enter 

 further into the question, nor extend the comparison to 

 extinct plants. In the following year I re-stated the 

 interpretation of Von Mohl and Williamson's comparison 

 (referred to in the next paragraph) with the Lepidoden- 

 dreae, in a short communication 7 to the British Association 

 at Sheffield, but the grounds for my opinion have not 

 been published in detail until now. 



The comparison of the root-bearing region of the 

 stock of Iscetes with the Stigmarian base of the Lepido- 

 dendroid trees had been made by Williamson 8 in 1887. 

 In his monograph on Stigmaria, by then recognised as 

 the root-bearing region of extinct plants belonging to 

 Lycopodiales, he refers to the interest of the similarity 

 between the roots themselves of Isoetes and Stigmaria 

 and also of the way in which they are borne. He states, 

 " In both organisms these rootlets are given off from the 

 lower part of a downward prolongation of a caulome, 

 which prolongation never develops leaves ; the rootlets, 

 therefore, are produced upon an axis which grew in the 

 opposite direction to that in which the leaf-bearing part 

 of the stem grew." 



The fundamental importance of this comparison be- 

 tween Isoetes and the Lepidodendreae is evident. How 

 completely it has passed into abeyance, however, is shown 

 by the fact that in recent discussions 9 of the mor- 



fi Bot. Gazette, 47, p. 311. 



7 British Ass. Report, 1910, p. 7S-J. 



s The Palaontographical Society . Vol. for 1SS6. (London, 1887.) 



'■' Only a general reference need be made to such works as Bower's 

 "Land Flora/' Scott's " Fossil Botany," and Seward's " Fossil Plants." 



