100 THE GEOLOGICAL HISTORY OF PLANTS. 



than herbaceous, and their appearance is quite different from that 

 of any true Algae, 



The type of Psilophyton is my P. princeps, of which the whole 

 of the parts and structures are well known, the entire plant being 

 furnished in abundance and in situ in the rich plant-beds of Gaspe. 

 A second species, P. robustius, has also afforded well-characterised 

 fructification. P. elegans, whose fruit appears as " oval scales," no 

 doubt bore sac-like spore-cases resembling those of the other species, 

 but in a different position, and perfectly flattened in the specimens 

 procured. The only other Canadian species, P. glabrum, being some- 

 what different in appearance from the others, and not having af- 

 forded any fructification, must be regarded as uncertain. 



The generic characters of the first three species may be stated as 

 follows : 



Stems dichotomous, with rudimentary subulate leaves, sometimes 

 obsolete in terminal branchlets and fertile branches ; and in decor- 

 ticated specimens represented only by punctiform scars. Young 

 branches circinate. Rhizomata cylindrical, with circular root- 

 areoles. Internal structure of stem, an axis of scalarifonn vessels 

 enclosed in a sheath of imperfect woody tissue and covered with a 

 cellular bark more dense externally. Fruit, naked sac-like spore- 

 cases, in pairs or clusters, terminal or lateral. 



The Scottish specimens conform to these characters in so far as 

 they are known, but not having as yet afforded fruit or internal 

 structure, they cannot be specifically determined with certainty. 

 More complete specimens should be carefully searched for, and will 

 no doubt be found. 



In Belgium, M. Crepin has described a new species from the 

 Upper Devonian of Condroz under the name P. Condrusianum 

 (1875). It wants, however, some of the more important characters of 

 the genus, and differs in having a pinnate ramification, giving it the 

 aspect of a fern. In a later paper (1876) the author considers this 

 species distinct from Psilophyton, and proposes for it a new generic 

 name Rhacophyton. 



The characters given by Mr. Carruthers, in his paper of 1873, for 

 the species P. Dechenianum, are very few and general : " Lower 

 branches short and frequently branching, giving the plant an oblong 

 circumscription." Yet even these characters do not apply, so far as 

 known, to Miller's fucoids or Salter's rootlets or Goeppert's Halise- 

 rites. They merely express the peculiar mode of branching already 

 referred to in Salter's Lepidodendron notTium. The identification of 

 the former plants with the Lepidodendron and Lycopodites, indeed, 



