l] DIFFICULTIES OF IDENTIFICATION. 11 



genera as with the structure of a recent forest tree. While 

 emphasizing the value of the microscopic methods of investiga- 

 tion, we are not disposed to take such a hopeless view of the 

 possibilities of the determination of fossil forms, in which no 

 internal structure is preserved, as some writers have expressed. 

 The preservation of minute structure is to be greatly desired 

 from the point of view of the modern palaeobotanist, but he 

 must recognise the necessity of making such use as he can of 

 the numberless examples of plants of all ages, which occur only 

 in the form of structureless casts or impressions. 



In looking through the writings of the earlier authors we 

 cannot help noticing their anxiety to match all fossil plants with 

 living species ; but by degrees it was discovered that fossils are 

 frequently the fragmentary samples of extinct types, which can 

 be studied only under very unfavourable conditions. In the 

 absence of those characters on which the student of living 

 plants relies as guides to classification, it is usually impossible 

 to arrive at any trustworthy conclusions as to precise botanical 

 affinity. Brongniart and other authors recognised this fact, 

 and instituted several convenient generic terms of a purely 

 artificial and provisional nature, which are still in general use. 

 The dangers and risks of error which necessarily attend our 

 attempts to determine small and imperfect fragments of extinct 

 species of plants, will be briefly touched on in another place. 



