202 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DcC. 14, 



and respiration ; and there is also another and a greater difficulty 

 not sufficiently \inderstood, namely, that the habit and functions of a 

 plant are not indicated by its structure to the extent which is com- 

 monly supposed. The prevalent tendency to infer from the lax and 

 compressible tissue of so many of the plants of the Carboniferous 

 flora, that the vegetation of that epoch was a swamp one, is one 

 instance of this amongst many. Amongst the marsh -trees of our 

 own era, whether of fresh water or salt, of the tropic or of the tem- 

 perate zones, the botanist perceives hard and compact woods to 

 prevail : this is shown in the Swamp-pines of the north and south 

 temperate hemispheres on the one hand, and in the Avice^mia, Bhi- 

 zophora, and other mangroves, and a host of dicotyledonous trees of 

 the deltas and salt-water creeks of the tropics, on the other. And if 

 we turn to the driest regions of the globe, the Baobab, one of the 

 most bulky known trees, an inhabitant of Senegal and of the arid 

 Cape de Verd, may almost be sliced with a knife, like a carrot*. 

 The gigantic Cacti of America and the EupJior'bifB of the African 

 deserts are other cases in point, of succulence indicating drought. 

 That the plants which contributed most materially to the formation 

 of coal, had unusually lax tissue, is, I think, proven ; but this, of 

 itself, is no argument for their being evidences of a swamp-flora ; 

 whilst the prevalence of ferns throughout the coal-formations is 

 rather against such an hypothesis, than in its favour. On the other 

 hand 1 think that the geological evidence in favour of the coal-plants 

 having grown in swamps is of itself conclusive, and opposed to no 

 botanical considerations of importance. 



2. Observations on the Chonetes comoides {Sowerby). 

 By Thomas Davidson, Esq., F.G.S. &c. 



[Plate VIII.] 



The external characters of Chonetes comoides have been carefully 

 described by several authors t, but little or nothing appears to have 

 been written on its internal arrangements. Sowerby's figure does 

 not convey a correct idea of the double area, fissure, and cardinal pro- 

 cess belonging to this species ; he simply represents a bivalve shell 



* Yet Adanson, arguing from their gigantic dimensions, pronounced some 

 specimens of tliis tree to be upwards of 3750 years old ! 



"f" Described as " Productus comoides " by Sowerby in the 4th vol. of the ' Min. 

 Con." (p. 31, pi. 329, 1S23); but it is not P. comoide?, Phill. (' Mount. Limestone,' 

 p. 213, pi. 7, fig. 4 which represents the P^-od. Cora). This mistake was hinted 

 at by Prof. M'Coy in p. 107 of his ' Synopsis of the Carb. Foss. of Ireland,' 1S44 ; 

 but the authors who have more particularly described the exterior of this remark- 

 able species are M. de Verneuil, ' Russia and the Ural ^lountains,' vol. ii. p. 241, 

 1845, — Count Keyserling, ' Reise in das Petschora-land,' p. 214, pi. C. figs. 1 a,b,c, 

 1846, — M. de Koninck, ' Monographic des Genres Productus et Chonetes,' p. 189, 

 pi. 19. fig. 1, I a, b, c, 1847 ; this excellent description of the exterior is accompa- 

 nied by a list of synonyms. 



