310 



PHYSIOLOGICAL BOTANV. 



PART II. 



(315.) Fossil Botany. The history of vegetation 

 could not be completed without some inquiry respecting 

 those plants which existed on the earth in its primaeval 

 state, during the extended geological epochs which 

 elapsed before the establishment of the present order of 

 things. Traces of this .ancient vegetation are very 

 abundant in certain strata, but more especially in the 

 " coal-measures," the important mineral combustible 

 obtained from them being nothing else than vegetable 

 matter in an altered and fossilized state. In general, we 

 do not find the remains of plants so perfectly preserved 

 as the skeletons of vertebrate animals, or the testaceous 

 coverings of mollusca. It is also rare to meet with 

 those parts (the flower and seeds) upon which the dis- 

 tinction of species and their classification chiefly depend : 

 but still the fragments which remain often possess very 

 great beauty ; and many specimens of wood are so exactly 

 preserved, that their tissue may be distinguished under a 

 microscope as completely as in recent species. As it is 

 principally from these fragments of stems, and the im- 

 pressions of leaves, that any comparison between the 



