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SECTION V. 



GENERAL REMARKS ON THE FOSSIL PLANTS REPRESENTED AND DESCRIBED 

 IN THIS WORK; WITH THEIR GENERIC AND SPECIFIC CHARACTERS AS 

 DERIVED FROM THEIR TISSUE. 



The first general remark which I have to offer respecting the fossil 

 vegetables figured in the Plates, is, that their concentric layers present the 

 same irregularity as those of our present trees, some of them being much 

 broader than others in the same specimen. An inference to be made from 

 this circumstance is, that the climate which existed at the epochs when 

 these vegetables grew, resembled ours in the irregularity of its successive 

 summers. If, at the present day, a warm and moist summer produces a 

 broader annual layer of wood than a cold or dry one, and if fossil plants ex- 

 hibit such appearances as we refer in recent plants to a diversity of sum- 

 mers, then it is reasonable to suppose that a similar diversity formerly pre- 

 vailed. The remark, however, applies only to the plants of the lias and 

 oolite. 



The Coniferae of the coal formation and mountain-limestone group have 

 few and slight appearances of the lines by which the annual layers are se- 

 parated ; which is also frequently the case with the trees of our present tro- 

 pical regions. It is therefore possible, that, at the epochs of these forma- 

 tions, the changes of season, as to temperature at least, were not abrupt. 



The cells of the fossil Coniferae, are generally much larger than those 

 of our present trees of the same family. Thus, Figs. 1, 2, 3, 4, 5, 6, 7 and 

 8, of Plate IX., which are enlarged in the same degree as Figs. 4, 5, 6, 7 

 and 8, of Plate I., have much larger meshes than the latter. Our observa- 

 tions on this subject, however, are not sufficiently numerous or correct, to 



