342 GALA MITES. [CH. 



lines of the upper sporangia of each whorl of sporangiophores, 

 the lower sporangia being hidden by the ring of linear bracts \ 

 On some portions of the specimen of fig. 89, J., it is possible to 

 recognise the outlines of cells on the coaly surface-film ; these 

 probably belong to the sporangium wall. This type of cone is 

 included under the genus Calamostachys, a name applied to 

 Calamitean strobili with certain morphological characters, as 

 described on p. 351. 



c. Roots. 



In 1871 Williamson^ described some sections of what he 

 considered to be a distinct variety of a Calamite stem. The 

 chief peculiarity which he noticed lay in the absence of 

 carinal canals, and in the solid pith. Some years later the 

 same observer^ came to the conclusion that the specimens were 

 probably those of a plant generically distinct from Galamites; 

 he accordingly proposed a new name Astromyelon. Subse- 

 quently Cash and Hick* gave an account of some examples of 

 apparently another form of plant, to which they gave the name 

 Myriophylloides Williams o ms ; and Williamson^ suggested the 

 term Helophyton as a more suitable generic designation. It 

 was, however, demonstrated by Spencer « that the plant de- 

 scribed by Cash and Hick was identical with Williamson's 

 Astromyelon. Williamson'' then gave an account of several 

 specimens of this type illustrating various stages in the growth 

 and development of the Astromyelon 'stems,' which he com- 

 pared with the rhizome of the recent genus Marsilia. 



In 1885 Renault^ published an account of Astromyelon in 

 which he brought forward good evidence in favour of regarding it 

 as a Calamitean root. The same author has recently given some 

 excellent figures and a detailed description of certain specific 

 types of these Calamite roots, and Williamson and Scott's 

 memoir on the roots of Galamites has rendered our knowledge 



i Vide Weiss (76), PI. m. and Weiss (84), p. 178. 



2 Williamson (71), p. 487, Pis. xxv. and xxvi. 



=^ Ibid. (78), p. 319, Pi. xix. * Cash and Hick (81), p. 400. 



5 Williamson (81), vide also Spencer (81). « Spencer (83), p. 459. 



7 Williamson (83), p. 459, Pis. xxvii.— xxx. « Kenault (85). 



