20 RELATION OF PALAEOBOTANY TO BOTANY AND GEOLOGY. [CH. 



afterwards discuss the importance of such types, from the point 

 of view of plant evolution. 



The botanist who would trace out the phylogeny of any 

 existing class or family, makes it his chief aim to discover 

 points of contact between the particular type of structure 

 which he is investigating, and that of other more or less closely 

 related classes or families. 



Confining himself to recent forms, he may discover, here and 

 there, certain anatomical or embryological facts, which suggest 

 promising lines of inquiry in the quest after such affinities as 

 point to a common descent. Without recourse to the evidence 

 afforded by the plants of past ages, we must always admit that 

 our existing classification of the vegetable kingdom is an ex- 

 pression of real gaps which separate the several classes of plants 

 from one another. On the other hand our recently acquired 

 and more accurate knowledge of such genera as have been 

 alluded to, has made us acquainted with types of plant 

 structure which enable us to fill in some of the lacunae in our 

 existing classification. In certain instances we find merged in 

 a single species morphological characteristics which, in the case 

 of recent plants, are regarded as distinctive features of different 

 sub-divisions. It has been clearly demonstrated that in 

 Lyginodendron, we have anatomical peculiarities typical of 

 recent cycads, combined with structural characteristics always 

 associated with existing ferns. In rare cases, it happens that 

 the remarkably perfect fossilisation of the tissues of fossil 

 plants, enables us not only to give a complete description of 

 the histology of extinct forms, but also to speak with con- 

 fidence as to some of those physiological processes which 

 governed their life. 



So far, palaeobotany has been considered in its bearings on 

 the study of recent plants. From a geological point of view 

 the records of ancient floras have scarcely less importance. In 

 recent years, facts have been brought to light, which show 

 that plants have played a more conspicuous part than has 

 usually been supposed as agents of rock-building. As tests of 

 geologic age, there are good grounds for believing that the 

 inferiority of plants to animals is more apparent than real. 



