OF PLANTS AND ANIMALS. 169 



mining genera and species, because it is founded on charac- 

 ters which have not been preserved, viz., the different parts 

 of the flower. Fossil plants are not so easily determined 

 as recent species, because their parts are usually separated 

 from each other. It is very seldom that any traces of their 

 reproductive organs are left. Fragments of stems, leaves, 

 and occasionally seeds, are the only data by which the plant 

 can be determined. We have to fall back, therefore, on 

 our knowledge of the natural system. There must be a 

 thorough acquaintance with the different natural orders, 

 and a familiarity with vegetable anatomy. There must 

 be a competent knowledge of the minute structure of all 

 the organs of plants, such as their root, stem, leaves, bark, 

 and fruit, and of the markings which they exhibit on their 

 exterior surface, together with some general ideas of the 

 vegetation of tropical climates as well as of cooler latitudes, 

 before the living affinities of the fossil plant can be deter- 

 mined. 



As fossil plants are generally found in detached frag- 

 ments, it is necessary to reconstruct the plant as completely 

 as possible, and to determine the relations of its several 

 portions to each other. It is evident that this must be a very 

 difficult task -, but it is a very necessary one, for the neglect 

 of it has led to a needless multiplication of fossil species, 

 portions of the same plant having been described as sepa- 

 rate species or genera. 



A knowledge of Comparative Anatomy is also necessary. 

 To a person unacquainted with this science it may appear 

 impossible, that from a single fragment of a fossil bone or 

 tooth, Naturalists are able to determine the general character 

 of its skeleton, and from thence to infer its appearance and 

 mode of life. Yet all this is true. If we find, for example, 

 a single fossil tooth, if it be a molar, it is sufficient to indi- 

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