138 HISTORICAL PALAZSONTOLOGY. 
stems and branches seem to have attained a height of two or 
three feet; and they sprang from prostrate “root-stocks” or 
Fig. 77.—Restoration of Pszio- 
phyton princeps. Devonian, Can- 
ada. (After Dawson.) 
creeping stems. Upon the whole, 
Principal Dawson is disposed to 
regard Pszlophyton as a ‘ general- 
ised type” of plants intermediate 
between the Ferns and the Club- 
mosses. Lastly, the Devonian de- 
posits have yielded the remains of 
the first actual ¢vees with which we 
“are as yet acquainted. About the 
nature of some of these (Ormoxylon 
and Dadoxylon) no doubt can be 
entertained, since their trunks not 
only show the concentric rings of 
growth characteristic of exogen- 
ous trees in general, but their 
woody tissue exhibits under the 
microscope the ‘‘ discs” which are 
characteristic of the wood of the 
Pines and Firs (see fig. 2). The 
singular genus /vofotaxites, how- 
ever, which occurs in an older por- 
tion of the Devonian series than * 
the above, is not in an absolutely 
unchallenged position. By Prin- 
cipal Dawson it is regarded as the 
trunk of an ancient Comzfer—the 
most ancient known; but Mr 
Carruthers regards it as more pro- 
bably the stem of a gigantic sea- 
weed. The trunks of Prototaxites 
(fig. 78, A) vary from one to three 
feet in diameter, and exhibit con- 
centric rings of growth; but its 
woody fibres have not hitherto 
been clearly demonstrated to pos- 
sess discs. Before leaving the 
Devonian vegetation, it may be mentioned that the hornstone 
or chert so abundant in the Corniferous limestone of North 
America has been shown to contain the remains of various 
microscopic plants (Diatoms and Desmids). We find also in 
the same siliceous material the singular spherical bodies, with 
radiating spines, which occur so abundantly in the chalk flints. 
and which are termed Xanthidia. These may be regarded 
