1522 



CORMOPHYTA. 



stems of the Sigillarians are marked by continuous longitudinal ribs, 



between which are the leaf-scars 

 (fig. 1 391), forming whorls round 

 the stems. It will be seen from 

 the figure that the arrangement 

 of these scars is such that each 

 one is placed in the interval be- 

 tween two scars of the horizontal 

 rows immediately above and be- 

 low ; this arrangement, or phyllo- 

 taxis, obtaining in all plants with 

 leaves forming whorls. The ex- 

 ternal coat of the stem is very 

 hard, beneath which is an inner 

 bark composed of cellular tissue 

 traversed by rope-like fibres, while 

 the woody central axis is small, 

 and somewhat intermediate in 

 structure between that of the Le- 

 pidodendroids and Gymnosperms. 

 The roots (Stigmaria) usually 

 Fig. i3 9 o.-Stem of a semi-erect sigiiiaria start from the stem in four main 

 Dawso°n!)" seam; * om N ° va Sc ° tia ' (Mter branches, which divide dichotom- 



ously several times, and then con- 

 tinue in long extensions, which Sir J. W. Dawson considers are 



Fig. 1391. — Part of stem of Sigiiiaria Utschneideri; from the Carboniferous. 

 The left-hand figure shows a small portion on a larger scale. 



intended to afford a firm support in a soft marshy soil. The root- 

 lets (fig. 1392) were arranged on the roots in whorls; and when 



