CARBONIFEROUS LYCOPODS AND SPHENOPHYLLS. 101 



equally clear that Stigmariopsis was the rhizome of some other 

 species of Sigillaria. In no case, however, where the rhizome has 

 been found attached to the trunk, has it been possible to deter- 

 mine satisfactorily the species to which the trunk belonged, 

 though the generic determination of several examples is placed 

 beyond dispute. 



Internal Organization. — Our first knowledge of the internal 

 structure of Sigillaria is due to Brongniart,' who in 1839 

 described a small specimen about 2 cm. long and 4 cm. in 

 diameter, which he identified as Sigillaria elegans." 



It consisted of a cortical cylinder, on whose outer surface the 

 leaf-scars were preserved, from which not only the genus but the 

 species has been identified. Within the cortex lay the vascular 

 cylinder, separated from it by a clear space, from which the 

 intervening tissue had decayed. The vascular cylinder was 

 composed of a number of distinct but contiguous vascular wedges, 

 forming a hollow cylinder about 14 mm. in diameter, but the 

 width of the vascular band itself was only 1 mm. The pith 

 which once filled this hollow cylinder had entirely disappeared. 

 Such is a general description of the arrangement of the parts of 

 the stem, which must now be considered in fuller detail. 



Vascidar Zone. — Each of the vascular wedges forming the 

 xylem portion of the stem is composed of two parts — the inner 

 primary or centripetally developed zone, and an exogenous or 

 centrifugally developed zone. 



In transverse section the primary bundles have the form of a 

 segment of a circle, whose convexity points towards the 

 centre of the stem. The tracheides composing it are arranged 

 without any definite order. The larger tracheides occupy the 

 inner part of the bundle, their walls being marked by transverse 



^ Observations sur la Structure int4rieure du Sigillaria elegans comparie 

 a cells de Levidodendron et des Stigmaria et a celle clex viqitaux vivanta. 

 Archives du Jifusexim, Vol. I., pp. 405-461, Pis. XXV. -XXXV. (I.-XI.). 

 1839. 



- This specimen was so identified by Brongniart in error. In reality it 

 appears to be his Sigillaria menardi, Hist. d. veget. foss., PI. CLVIII., fig. 

 6 (?not fig. 5), which again is only a young state of Sigillaria Brardii, 

 Brongt., the type of the Clathraria Section of Sigillaria. See Zeiller, 

 Ann. d. Scieni Nat., 6« Ser. Bot., Vol. XIX., p. 259, 1SS4; also Weiss, 

 Sitz. Bericht d. Gesell. natur Freunde., Berlin, No. 5, p. 70. 18S6. 



