52 THE THEOKY OF EVOLUTION 



conditions which may be easily noted in the same 

 decayed stem. In all these conditions we find fossil 

 trees. Flowers are really only known to us by enclosure 

 in amber (fossil resin) (Fig. 11). 



Nevertheless it is possible, though certainly only 

 on rough lines, to conceive an idea of the succession of 

 series and the connection of the greater groups, of the 

 process of transformation within separate types and in 

 some degree also of the reasons and causes of same. 



1. Brief purview of the chronological succession of 

 the larger plant groups. 



Gothan adopts, for the history of plant life, 

 a somewhat different limitation of the three chief 

 periods, quite logically according to the principles 

 which we have treated more in detail above. 1 



According to this the Palaeozoic era closes with 

 the lower Permian, the Mesozoic with the lower Chalk 

 where the Caenozoic commences. 



(1) Oldest discoveries of plants. 



According to Gothan 2 the graphite masses which 

 are found even in the Primary rocks (gneiss and Primary 

 slate) point with certainty to the existence of organic 

 growths. Although one might be inclined, owing to 

 the dependence of the animals upon plants, to deduce 



1 The first appearance of new types, high development, and predomin- 

 ance of previously sparsely represented ones or disappearance of other 

 previously most diversified forms. (See above, p. 24.) 



2 Dr. W. Gothan : Entwicklung der Pflanzenwelt, Osterwieck am Harz, 

 1909, p. 15. 



