4 ANCIENT PLANTS 



As we follow their histories we shall see how family- 

 after family has risen to dominate the forest, and has in 

 its turn given place to a succeeding group. Some of the 

 families that flourished long since have living descendants 

 of dwarfed and puny growth, others have died out com- 

 pletely, so that their very existence would have been 

 unsuspected had it not been revealed by their broken 

 fragments entombed in the rocks. 



From the study of the fossils, also, we can discover 

 something of the course of the evolution of the different 

 parts of the plant body, from the changes it has passed 

 through in the countless ages of its existence. Just as 

 the dominant animals of the past had bodies lacking in 

 many of the characters which are most important to the 

 living animals, so did the early plants differ from those 

 around us to-day. It is the comparative study of living 

 and fossil structures which throws the strongest light on 

 the facts and factors of evolution. 



When the study of fossil organisms goes into minute 

 detail and embraces the fine subtleties of their internal 

 structure, then the student of fossil plants has the ad- 

 vantage of the zoological observer, for in many of the 

 fossil plants the cells themselves are petrified with a 

 perfection that no fossil animal tissues have yet been 

 found to approach. Under the microscope the most 

 delicate of plant cells, the patterns on their walls, and 

 sometimes even their nuclei can be recognized as 

 clearly as if they were living tissues. The value of this 

 is immense, because the external appearance of leaves 

 and stems is often very deceptive, and only when both 

 external appearance and internal structure are known 

 can a real estimate of the character of the plant be 

 made. In the following chapters a number of photo- 

 graphs taken through the microscope will show some 

 of the cell structure from fossil plants. Such figures 

 as fig. 1 1 and fig. 96, for example, illustrate the excel- 

 lence of preservation which is often found in petrified 

 plant tissues. Indeed, the microscope becomes an essen- 



