COMMENCEMENT OF LAND PLANTS. 47 



diameter of about three feet, while the leaves measured 

 twenty inches in length. In the forests of the coal era, the 

 lepidodendra would enjoy the rank of firs in our forests, 

 affording shade to the only less stately ferns and calamites. 

 The internal structure of the stem, and the character of the 

 seed-vessels, show them to have been a link between single- 

 lobed and double-lobed plants a fact worthy of note, as it 

 favours the idea of a progress in vegetable creation, in the 

 line of an improved organization. It is also curious to find a 

 missing link of so much importance in a genus of plants 

 which has long ceased to have a living place upon earth. 



The other leading plants of the coal era are without re- 

 presentatives on the present surface, and their characters are 

 in general less clearly ascertained. Amongst the most re- 

 markable are the sigillaria, of which large stems are very 

 abundant, showing that the interior has been soft, and the 

 exterior fluted, with separate leaves inserted in vertical rows 

 along the flutings and the stigmaria, a plant apparently cal- 

 culated to flourish in marshes, or pools, having a short, thick, 

 fleshy stem, with a dome-shaped top, from which sprung 

 branches of from twenty to thirty feet long. Amongst mono- 

 cotyledons were some palms, (flabellaria and nceggerathia?) 

 besides a few not distinctly assignable to any class. 



The conifers of the coal are comparatively rare, and are 

 only as yet found in isolated cases, and in sandstone beds. 

 One discovered in the Craigleith quarry, near Edinburgh, 

 consisted of a stem about two feet thick, and forty-seven feet 

 in length. Others were afterwards found, both in the same 

 situation, and at Newcastle. Leaves and fruit, being wanting, 

 an ingenious mode of detecting the nature of these trees was de- 

 . vised by some naturalists residing in the northern capital.( 26 ) 

 Taking thin polished cross slices of the stem, and sub- 

 jecting them to the microscope, they detected the structure of 

 the wood to be that of a cone-bearing tree, by the presence of 

 certain " reticulations" which distinguish that family, in addi- 

 tion to the usual radiating and concentric lines. That par- 

 ticular tree was concluded to be an araucaria, a species now 

 found in Norfolk Island, in the South Sea, and in a few other 



