OF THE DIFFERENT TRIBES OF PLANTS. 17 



during these modifications. In general, the calcareous matter has crystal- 

 lized in divergent prisms, and has thus given rise to a kind of cellular ap- 

 pearance, very readily distinguishable from the true, but which a novice 

 might be apt to consider as the regular texture of a cellular or agamic 

 plant ; while the siliceous or calcedonic has arranged itself in parallel un- 

 dulations or series of curves. The appearances produced by the two modes 

 of crystallization are very distinct, insomuch that a person might, in many 

 cases, pronounce with accuracy as to the infiltrated substance, without using 

 any other means of detecting it than ocular inspection. 



The regularity of structure displayed by many fossils is truly astonish- 

 ing. Many of them exhibit an internal texture as perfect as can be ob- 

 tained from the most delicate sections of a recent plant. The structure 

 thus disclosed often corresponds so precisely with that of recent stems, that 

 one can scarcely hesitate to refer the one and the other to the same genus, 

 although the differences exhibited by recent species of a genus are often so 

 slight, that there appears little hope of our being able to distinguish fossil 

 species by their internal structure, without including other characters. 



The remarks which I have now to offer respecting the characters pre- 

 sented by the woody stems of plants, are illustrated by figures, which will 

 be found in the first and second plates. 



PLATE I. 



This Plate contains representations of the internal structure of Recent 

 Plants belonging to the Gymnospermous Phanerogamic, Monocotyledonous 

 Phanerogamic, and Dicotyledonous Phanerogamic Classes, to which we re- 

 quire more particularly to attend, in attempting to determine the organiza- 

 tion of the fossil plants to be described. The portions represented are of 

 very thin transverse or horizontal slices, viewed by transmitted light, and 

 magnified about fifty times. 



Fig. I . represents the Monocotyledonous stem, being copied from a por- 



