720 CHAKACTEES OF FOSSIL PLANTS. 



that the fossil botanist can draw conclusions. Besides this, fossil 

 vegetables, thus reduced to some of their insulated organs, scarcely 

 ever present them in such a state of preservation as to allow them to 

 be studied in all their constituent parts. Sometimes the internal 

 structure of the stem can be traced, and by examination under the 

 microscope the nature of its woody tissue may be determined. In 

 this way some fossilised woods have been referred to the Coniferous 

 tribe, in consequence of the presence of punctated woody tissue 

 (figs. 904-907). Fossil woods have been shown by chemical;tests to 

 contain portions of vegetable tissue, cemented into a mass by silica. 

 In some cases the vessels and cells are separately silicified without 

 being united into a compact mass. In these instances the wood breaks 

 down easily. At times the internal structure is obliterated,, and it is 

 only from the external configuration, the nature of the outer covering, 

 and the scars of the leaves, that any conclusions can be drawn. The 

 leaves often furnish important and valuable characters, and, in the 

 case of fossil ferns, their form, divisions, and venation, supply distin- 

 guishing marks. The leaves, however, are generally isolated, and are 

 rarely found in connection with the stems. Thus, the separation of 

 the different parts of the plant, and, in most cases, their imperfect 

 state of preservation, are great obstacles to the determination of fossil 

 plants by, a comparison with those which now exist on the earth. 

 Before, then, endeavouring to compare a fossil vegetable with living 

 vegetables, it is necessary to put together, with as much exactness as 

 possible, according to the parts preserved, and the general data of 

 vegetable anatomy and organography, the portions of the plant under 

 examination ; to contrast these portions with the other organs of the 

 same plant, searching for their points of attachment, their forms and 

 vascular connections, being guided generally by traces of structure 

 rather than by exterior form ; and by endeavouring to reconstruct a 

 vegetable by bringing together all fragments from the same fossil beds, 

 which may belong to the same plant. The connection of the different 

 parts of the same plant is of the greatest importance in vegetable 

 palaeontology, as from their fragmentary nature many difiBculties arise. 

 These difficulties are increased as we go back to the earliest geological 

 epochs, for the farther they are removed from the present state of 

 things, the greater are the differences between the fossil and living 

 plants. Dr. Hooker remarks, that the knowledge of recent botany 

 required to throw light upon the study of fossil plants, and the origin 

 of coal, must be both varied and extended. " Some acquaintance with 

 systematic botany is the first requisite ; through this alone can any 

 approximation to the living aflnities of the fossil be obtained. It 

 should embrace not only a knowledge of the principal groups, or 

 natural orders under which aU plants are arranged, but a familiarity 

 with vegetable anatomy; for when the stem or trunk alone is preserved 



