342 HOW PLANTS LIVE AND WORK. 



rocks contain specimens of plants which differ to no very marked 

 extent from those alive at the present time ; but as the botanist 

 examines rocks of older date, he finds records of plants which 

 depart very widely from the living species with which he is familiar. 

 For example, much of the black rock we know as coal may be 

 split into thin leaves, and when the pages of these leaves are care- 

 fully inspected they are seen to be covered with records of ancient 

 life and climate. Stem, root, and spore-cases are there, with all 

 their sharpness of outline unimpaired ; the delicate tracery of 

 frond and leaf is visible, as clear and fresh as if made yesterday. 

 And such rocky herbaria tell us in unmistakable terms that our 

 forest trees are parvenus, and that our humble Daisy is one of the 

 greatest upstarts in existence. 



It was from evidence of this kind that biologists were driven to 

 the conclusion that the present forms of plant life represent merely 

 a passing phase, to be succeeded in all probability by forms dif- 

 fering as widely from them as they themselves differ from the 

 extinct species preserved in the rocks. It became clear that the 

 earliest plants were probably exceedingly simple, and that they 

 were succeeded by more complex forms, which gradually led up to 

 those at present living. Notwithstanding this, it was generally 

 supposed that each species was the result of a distinct creative 

 act, and that the extinction which had clearly overtaken various 

 races of plants in the past was due to catastrophes which had 

 suddenly overwhelmed them. A few naturalists, however, came 

 to the conclusion that the evidence of the rocks pointed to a 

 process of gradual evolution, by which recent species had been 

 derived from pre-existing ones by direct descent; but to what 

 causes this process, if it existed, was due, they were unable to 

 suggest. Matters were in this rather unsatisfactory state when, on 

 October ist, 1859, Darwin's book on The Origin of Species was 

 published. In this epoch-making work, the author not only laid 

 down the fundamental doctrine *' that the innumerable species, 

 genera, and families of organic beings with which the world is 

 peopled have all descended, each within its own class or group, 

 from common parents, and have all been modified in the course of 

 descent," but he gave very sound reasons for supposing that such 

 modification had been brought about. 



