492 PAL/EOBOTANY. 



vessels, and separated by medullary rays. Outside the woody 

 axis is an inner bark composed of long durable fibres of 

 " bast-tissue," the whole surrounded by a thick outer bark of 

 dense cellular tissue. " The trunk when old lost its regular 

 ribs and scars, owing to expansion, and became furrowed like 

 that of an Exogenous tree." The roots, as will be seen im- 

 mediately, constitute the fossils known as Stigmaria. The 



Fig. 388. Fragment of Sigillaria Greeseri. The left-hand figure shows a small 

 portion enlarged. Carboniferous. 



leaves are believed to be the so-called Cyperitcs, long, narrow, 

 rigid, and two- or three- nerved. The fruits are supposed to 

 be Trigonocarpa, " borne in racemes on the upper part of the 

 stem." Upon the whole, Dr Dawson is disposed to adopt the 

 view, originally put forth by Brongniart, that the Sigillaricc 

 find their nearest living allies in the Cycads, and that if not 

 actually referable to the Gymnospermous Exogens, they may 

 be intermediate between these and the higher Acrogens. 



Mr Carruthers, on the other hand, describes Sigillaria as 

 consisting of a central cellular pith or medulla, surrounded by 

 a sheath consisting wholly of scalariform vessels, the whole 

 enveloped in an external cortical mass of cellular tissue. The 

 medullary sheath is perforated by meshes for the passage out- 

 wards of the vascular bundles which go to the axial appendages 

 (the leaves and branches) ; but there are no true medullary 

 rays. Upon these grounds, Mr Carruthers decides against 

 the view that Sigillaria is a Gymnospermous Exogen, and he 

 regards it as Cryptogamic and Lycopodiaceous. He also dis- 



