XVl] SIGILLARIA 215 



elements, s, surrounds numerous scattered transfusion tracheae, t, 

 and below the two xylem strands, x, which are embedded in 

 delicate parenchyma there is a crescentic band of dark tissue, a, 

 resembling the smaller strand, a, in fig. 142, A', and the secre- 

 tory zone tissue of a Lepidodendron stem. 



iii. Fertile shoots of Sigillaria. 



Eeference has already been made to the manner of occur- 

 rence of strobili on Sigillarian stems ; it remains to describe the 

 structure of these reproductive shoots. Sigillariostrobus, the 

 name given to Sigillarian strobili, may be defined in general 

 terms as follows : 



Cylindrical cones, rarely dichotomously branched^ as in 

 species of Lycopodium and Selaginella, which may reach a 

 length of 30 cm. {e.g. Sigillariostrobus nobilis Zeill.^) and a 

 diameter 2 — 5 cm. ; peduncle long and slender, sometimes 

 bearing acicular bracts or, after leaf-fall, characterised by leaf- 

 cushions and leaf-scars like those on vegetative shoots 

 (fig. 201, E). The stalked cones are borne in irregular verticils 

 and in some species in vertical series, the fertile zones being 

 separated by comparatively long sterile portions of the stem 

 (fig. 199). The cones were deciduous and, in certain cases if 

 not in all, the individual sporophylls became detached from 

 the cone-axis on maturity. The slender axis bore spiral or 

 verticillate imbricate sporophylls attached at right angles or 

 more or less obliquely. The basal rhomboidal portion bore 

 spores on its upper surface (fig. 201, F), presumably enclosed 

 in a somewhat radially elongated sporangium (fig. B) and was 

 prolonged distally into a narrow lanceolate free portion, in some 

 species with a ciliate border (fig. D). The sporangia probably 

 produced megaspores and microspores, but such spores as have 

 been recognised appear to belong to the former category. The 

 designation Triletes is applied to isolated spores of Sigillaria or 

 to those of Lepidodendron. 



Sigillariostrobus Tieghemi Zeiller^ (figs. 201, E, F). In this 



1 Goldenberg (55) ; Kidston (97). ^ Zeiller (88) A. PI. xo. 1, p. 598. 



» Zeiller (84) ; (88) A. PL Lxxxix. 



