170 HISTORICAL PALAEONTOLOGY. 



is marked with numerous rhombic or oval scars, arranged in 

 quincunx order, and indicating the points where the long, 

 needle-shaped leaves were formerly attached. The fruit con- 

 sisted of cones or spikes, carried at the ends of the branches, 

 and consisting of a central axis surrounded by overlapping 

 scales, each of which supports a " spore-case " or seed-vessel. 

 These cones have commonly been described under the name 

 of Lepidostrobi. In the structure of the trunk there is nothing 

 comparable to what is found in existing trees, there being 

 a thick bark surrounding a zone principally composed of 

 " scalariform " vessels, this in turn enclosing a large central pith. 

 In their general appearance the Lipidodendra bring to mind 

 the existing Araucarian Pines ; but they are true " Crypto- 

 gams, " and are to be regarded as a gigantic extinct type of the 

 modern Club-mosses (Lycopodiacea). They are amongst the 

 commonest and most characteristic of the Carboniferous 

 plants ; and the majority of the " spore-cases " so commonly 

 found in the coal appear to have been derived from the cones 

 of Lepidodendroids. 



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 longitud- 

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

 indicating 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, accord- 

 ing to Dawson, partly of the disc-bearing fibres so characteristic 

 of Conifers ; but, according to Carruthers, entirely made up of 

 the " scalariform " 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, stand- 



