370 



PALEOZOIC SYSTEM OF ROCKS. 



scription is like the Lepidodendron, except that the woody cylinder is 

 larger and thicker ; but closer examination shows, in addition, the 



woody cylinder divided into woody 

 wedges by medullary rays, g g, in 

 true exogenous style, though the 

 H Hf* concentric rings characteristic of 

 Exogens are wanting. Still closer 

 examination with the microscope 

 shows a true gymnospermous tis- 

 sue (page 328, Figs. 389 to 391), 

 both on cross and longitudinal sec- 

 tion. Now, there is no plant living 

 which combines gymnospermous 

 tissue with a general stem-structure 

 at all similar to this, except Cycads 

 (Cycas, Zamia, etc.). For the sake 

 of comparison, we have given (Fig. 

 507) a cross-section of a Cycas; 

 the letters represent the same as in 

 the previous figure. There can be 



Fia. 505.-Restoration of Sigillaria, by Dawson. n0 reaS Onable doubt, therefore, of 



the close alliance of the Sigillarids with the Cycads. But their close 

 connection with Lepidodendrids shows an equally close, or closer, alli- 



Fig. 506. — Ideal Section of a Sigillaria-Stem: a, pith; 

 b, woody cylinder; c, inner bark; d, rind; e, bases 

 of leaves; /, vascular thread running to the 

 leaves; g, medullary rays. 



Fig. 507.— Cross-Section of 

 Stem of Cycas. 



ance with Lycopods. So thoroughly are they a connecting type that 

 some paleontological botanists (Dawson) regard them as Cycads with 

 strong Lycopod affinities, while most regard them as Lycopods with 

 strong Cycad affinities. Recent investigations seem to substantiate the 

 latter view ; for, in connection with Sigillaria, inflorescence similar to 

 that of Lepidodendrons, and containing spores, have been at last found.* 

 5. Calamites. — These are plants having long, slender, tapering, reed- 



* Annales des Sciences Botarriques, vol. xix, p. 256, 1884. 



