Mr Witham's Observations on Fossil Vegetables. 185 



more immediately connected with the object of the publication 

 is the third, in which the skilful author thus unfolds his plan, 



" Hitherto, the attention of geologists has been exclusively 

 confined to the external forms of fossil plants ; and these forms, 

 illustrated by reference to living species, and to vegetable 

 anatomy, have afforded characters by which numerous species 

 and genera may be distinguished with accuracy. But the sup- 

 posed destruction of the internal structure of most fossil plants, 

 and the difficulty of applying the microscope to those which 

 evidently retain it, have hitherto prevented our becoming ac- 

 quainted with the organization of these plants. Many fossil 

 vegetables are converted into a mass of carbonaceous matter : 

 others are filled with up sand, and other substances, the external 

 part, or cortex, alone remaining ; but it has been found that 

 many retain their original structure, the interstices being filled 

 up by calcareous or siliceous crystallizations. A method has 

 lately been discovered, by which the organization of the latter 

 may be satisfactorily examined." 



A number of beautiful plates, amounting to six in number, 

 thenfollow, containing "representations of the internal structure 

 of Recent and Fossil Plants belonging to the Gymnospermous 

 Phanerogamic, Monocotyledonous Phanerogamic, and Dico- 

 tyledonous Phanerogamic Classes. The portions represented 

 are of very thin slices, viewed by transmitted light and magni- 

 fied about fifty-five times. 



Into the details of description connected with the internal 

 structures thus described, we are precluded from entering ; 

 nor, indeed, could we well make them intelligible to our read- 

 ers without the aid of Mr Witham's valuable plates. We shall 

 therefore hasten to the last section, in which the author's con- 

 clusions are explained. 



" The first general remark which I have to offer respecting 

 the fossil vegetables figured in the Plates, is, that their con- 

 centric layers present the same irregularity as those of our re- 

 cent plants. An inference to be made from this circumstance 

 is, that the climate which existed at the epochs when these ve- 

 getables grew, resembled ours in the irregularity of its succes- 

 sive summers. If, at the present day, a warm and moist sum- 

 mer produces a broader annual layer of wood, than a cold or 

 dry one, and if fossil plants exhibit such appearances as we 



