168 HISTORICAL PALAEONTOLOGY. 



The so-called Sigillarioids, represented mainly by Sigillaria 

 itself (fig. in), were no less abundant and characteristic of the 

 Carboniferous forests than the Lepidodendra. They commence 

 their existence, so far as known, in the Devonian period, but 

 they attain their maximum in the Carboniferous ; and unlike 

 the Lepidodendroids they are not known to occur in the 

 Permian period. They are comparatively gigantic in size, 

 often attaining a height of from thirty to fifty feet or more ; 

 but though abundant and well preserved, great divergence of 

 opinion prevails as to their true affinities. The name of Sigil- 

 larioids (Lat. sigilla, little seals or images) is derived from the 

 fact that the bark is marked with seal-like impressions or leaf- 

 scars (fig. in). 



Externally, the trunks of Sigillaria present .strong longitudinal 

 ridges, with vertical alternating rows of oval leaf- scars indicating 



Fig. in. Fragment of the external surface of Sigillaria Grosser!, showing the ribs and 

 leaf-scars. The left-hand figure represents a small portion enlarged. Carboniferous, 

 Europe. 



the points where the leaves were originally attached. The trunk 

 was furnished with a large central pith, a thick outer bark, and 

 an intermediate woody zone, composed, according to Dawson, 

 partly of the disc-bearing fibres so characteristic of Conifers ; 

 but, according to Carruthers, entirely made up of the " scalari- 

 form " vessels characteristic of Cryptogams. The size of the 

 pith was very great, and the bark seems to have been the most 

 durable portion of the trunk. Thus we have evidence that 

 in many cases the stumps and " stools" of Sigillaria, standing 



