268 LYCOPODIALES [CH. 



Stigmaria-like rootlets spread into the surrounding shale. At 

 a higher level the fissured bark shows indistinctly defined 

 leaf-cushions which pass gradually upwards into cushions 

 and scars arranged in closer order on regular vertical ribs. 

 The surface-features in this region are practically those of a 

 ribbed Sigillaria. Traced farther upwards the vertical ribs 

 die out and cushions of the Lepidodendroid form cover the 

 surface of the bark. The leaf-scars, with a supraposed ligular 

 pit and two vertically elongated parichnos-scars, are said to bear 

 a closer resemblance to those of Sigillaria and Bothrodendron 

 than to the leaf-areas of Lepidodendron. Nothing is known as 

 to the anatomy of this stem, nor have fertile shoots been 

 discovered. In the absence of more trustworthy evidence than 

 is available conclusions of a phylogenetic nature must be 

 accepted at their true value. It is however legitimate to 

 describe Archaeosigillaria primaeva as one of the oldest 

 examples of a lycopodiaceous plant which shows well-preserved 

 external features, and these are of exceptional interest as 

 indicating a combination of generic characters. This Devonian 

 type lends support to the view that Lepidodendron and Sigillaria 

 are offshoots, dififering from one another in comparatively 

 unimportant points, from a common ancestral type. 



The generally accepted statement that arborescent Palaeo- 

 zoic Lycopodiales bore their sporangia on specially modified leaves 

 (sporophylls) grouped in cones which were usuallyproduced at the 

 tip of slender branches, has recently shared the fate of most rules. 

 Prof Bower in his Origin of a Land Flora mentions a Belgian 

 specimen oi Finakodendron mv^ivum Weiss from the Westphalian 

 series (Middle Coal-Measures), to be described by Dr Kidston, 

 which bore its sporangia " associated with the leaves of certain 

 portions of the stem, without any cone-formation. The fertile 

 and sterile portions are distinguished only by the presence or 

 absence of sporangia'." 



Lepidodendron and Sigillaria can hardly be claimed as the 

 direct ancestors of any existing type of Lycopodiales, but while 

 exhibiting points of contact with Lycopodium, Selaginella, and 

 Psilotum they are perhaps more closely allied to Isoetes. 



1 Bower (08) p. 305. 



