FOSSIL PLANTS AS RECORDS 169 



again by cultivation; while in the Paleozoic period 

 Lepidodendron seemed to stretch wellnigh from pole to 

 pole. 



The importance of the relation of plant structure to 

 the climate and local physical conditions under which it 

 was growing cannot be too much insisted upon. Modern 

 biology and ecology are continually enlarging and render- 

 ing more precise our views of this interrelation, so that 

 we can safely search the details of anatomical structure 

 of the fossil plants for sidelights on the character of the 

 countries they inhabited and their climates. 



It has been remarked already that most of the fossils 

 which we have well preserved, whether of plants or 

 animals, were fossilized in rocks which collected under 

 sea water; yet it was also noted that of marine plants 

 we have almost no reliable fossils at all. How comes 

 this seeming contradiction? 



The lack of marine plant fossils probably depends on 

 their easily decomposable nature, while the presence ot 

 the numerous land plants resulted from their drifting out 

 to sea in streams and rivers, or dropping into the still 

 salt marshes where they grew. Hence, in the rocks 

 deposited in a sea, we have the plants preserved which 

 grew on adjacent lands. In fresh water, also, the plants 

 of the neighbourhood were often fossilized; but actually 

 •on the land itself but little was preserved. The winds 

 and rains and decay that are always at work on a land 

 area tend to break down and wash away its surface, not 

 to build it up. 



There are many different details which are used in 

 •determining the evidence af a fossil plant. Where leaf 

 invpressions are preserved which exhibit a close similarity 

 to living species (as often happens in the Tertiary period), 

 it is directly assumed that they lived under conditions 

 like those under which the present plants of that kind 

 are living; while, if the anatomy is well preserved (as 

 in the Palaeozoic and several Mesozoic types), we can 

 compare its details with that of similar plants growing 



