80 



'J'KANSACTTONS, NATUHAL HISTORY SOCIETY OF GLASGOW. 



after a critical examination of the subject, rejects the triach 

 theory of their formation. 



It may be noted that it is not by any means clear that all 

 the specimens described by Renault under the name of Stigmaria 



really belong to that 

 plant. In a few cases 

 his identification is open 

 to great doubt. 



Notwithstanding the 

 adverse criticism to the 

 view promulgated by 

 MM. Renault and 

 Grand 'Eury, these 

 authors still believe in 

 some Stigmaria being 

 rhizomes and others true 

 roots. Grand 'Eury in 

 his Geologic et Faleont- 

 ologiedu Basshi Houiller 

 du Gard,^ makes the 

 following remarks on 

 Stigrnar'ia, which I give 

 in full. I do not see, 

 however, that any 

 further data is given in 

 support of the statement 

 again brought forward. 

 The figures given in illustration appear to be rather in the form 

 of diagrams than of carefully executed illustrations of individual 

 specimens, and there is an absence of any definite proof of a 

 single case of Sigillarian stem having been developed from 

 Stigmaria as the product of a bulb: — - 



" Those constant in diameter, with cicatrices disposed in regular 

 quincunc are the rhizomes; the other, short, very variable in 

 diameter, the roots of Sigillaria, to the base of which one often 



1 P. 236. St. ^tienne, 1890. 



^ In Britain all the stems which have shown the rhizome attached to 

 their base have been true Stigmaria, even according to the description 

 given by these authors. 



Fig. 13, — Stigmaria. Transverse section of 

 portion of vascular cj'linder, showing irregu- 

 lar development of tracheides at a and a. 

 Specimen from Oldham (Slide No. 565a). 



