174 



THE GEOLOGICAL HISTORY OF PLANTS. 



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"Their thick stems, marked nith linear scars and having two 

 rows of large depressed areoles on the sides, suggest no affinities to 

 any known plants. They are usually ranked with Lepidodendron 

 and Ulodendron, but sometimes, and probably with greater reason, 

 are regarded as allied to tree-ferns. At the Joggins a very fine 

 species (Jf. magnificum) has been found, and at Sydney a smaller 

 species (M. humile) ; but both are rare and not well preserved. If 

 the large scars bore cones and the smaller bore leaves, then, as Bron- 

 gniart remarks, the plant would much resemble Lepidophloios, in 

 which the cone-scars are thus sometimes distichous. But the scars 

 are not round and marked with radiating scales as in Lepidophloios; 

 they are reniform or oval, and resemble those of tree-ferns, for which 

 reason they may bo regarded as more probably leaf-scars ; and in 

 that case the smaller linear scars would indicate ramenta, or small 

 aerial roots. Further, the plant described by Corda as Zippea die- 

 ticha is evidently a Megaphyton, and the structure of that species is 

 plainly that of a tree-fern of somewhat peculiar type. On these 

 grounds I incline to the opinion of Geinitz that these curious trees 

 were allied to ferns, and bore two rows of large fronds, the trunks 

 being covered with coarse hairs or small aerial roots. At one time I 

 was disposed to suspect that they may have crept along the ground ; 

 but a specimen from Sydney shows the leaf-stalks proceeding from 

 the stem at an angle so acute that the stem must, I think, have been 

 erect. From the appearance of the scars it is probable that only a 

 pair of fronds were borne at one time at the top of the stem ; and, if 

 these were broad and spreading, it would be a very graceful plant. 

 To what extent plants of this type contributed to the accumulation 

 of coal I have no means of ascertaining, their tissues in the state of 

 coal not being distinguishable from those of ferns and Lyco- 

 podiacecey 



• 16. For descriptions of the genus Archmopteris and other Erian 

 ferns, see Chapter III. ,. 



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