224 LYCOPODIALES [CH. 



this is a distinction of doubtful' value. The division of the 

 primary xylem into separate strands in some stems of Sigillaria 

 of the Clathrarian and Leiodermarian forms is a characteristic 

 peculiarity; but 8. spinulosa forms a connecting link between 

 this type and the continuous arrangement of the xylem in 8. elon- 

 gata and 8. elegans. Kidston^ has shown that the discontinuous 

 primary xylem occurs in Lower Permian species, a fact con- 

 sistent with the view that the greater abundance of the 

 centripetally developed wood, characteristic of the older species, 

 represents a more primitive feature. This is not merely a 

 conclusion drawn from a consideration of geological age, but it 

 is in harmony with the view expressed by Scott^ that as plants 

 achieved greater success in producing secondary centrifugal 

 wood, the retention of any considerable quantity of primary 

 xylem became superfluous. As yet we know very little of 

 the structure of the perixylic tissues of Sigillaria, but there 

 is no sufficient reason for supposing that these differ in 

 essentials from those in Lepidodendron. The middle and outer 

 cortical tissues are practically identical in the two genera. The 

 parichnos is of the same type, except that in Sigillaria it 

 reached greater dimensions in the outer part of its course. 



V 



Sigillaria Brardi^ Brongniart. 

 Figs. 196, A— C; 200; 203. 



1822. Clathraria Brardi, Brongniart, Classif. V^g. foss., PI. xii. fig. 5. 

 1828. Sigillaria Brardi, Brongniart, Hist. V^g. foss. p. 430, PI. CLViii. 



fig. 4. 



S. Menardi, ibid. PI. clviii. 

 1836. Lepidodendron Ottonis, Geeppert, Fossil Farnkr. PI. XLii. 

 1839. S. elegans, Brongniart, Arch. Mus. Nat. Hist. Paris, Vol. I. 



p. 406, PI. XXV. 

 1849. S. spimdosa, Germar, Verstein. Wettin und Lobejiin, p. 59, 



PI. XXV. 



1893. S. mutans, Weiss, Abhand. Preuss. Geol. Anst. [N.F.] Heft 2, 



PI. VIII. 



1 Kidston (05) p. 547. 2 Soott, D. H. (02). 



3 For fuller synonymy ,rBee Kidston (86) A. p. 179 ; and Zeiller (06) p. 160 • 

 Koehne (04) p. 62. / r , 



