Chapter II —13— History 



all the species which can live there without man's protection. These are facts, one has 

 been wont to say. Yes, there are facts, but why these facts? What are their causes- 

 possible, probable, or certain? . . . And if, on the basis of the present distribution of 

 species and of a knowledge of climatic conditions, one could come to understand their 

 original distribution, would that not be a splendid achievement of science? 



"These important questions were for a long time a mystery to me. But I was far from 

 inclined to fight shy of them, as some authors have done. On the contrary ,_ these questions 

 attracted me, tormented me. I perceived neither solutions nor ways to arrive at solutions. 



"Fortunately, the advances in geology have shed on natural science a new light. 

 This light, no doubt, began as a feeble glimmer, but one penetrating every\vhere. Now it 

 is becoming larger; it shows us extensive vistas, entirely new. We can try to go back m 

 the chain of times to the origin of the vegetable and animal kingdoms. We have come to 

 the conclusion that the living organisms of our epoch have passed through diverse cU- 

 matic conditions and past geographical conditions no less varied. Thus, when the present 

 distribution of species seems odd to us, when it does not conform to modern climatic con- 

 ditions, it is probable that this is the effect of former geological and physical conditions. 

 We see here only the result of a different order of things, which in its turn was the conse- 

 quence of still different preceding conditions. 



"From this new point of view botanical geography ceases to be a simple accumulation 

 of facts. It occupies, on the contrary, an imposing position in the center of the sciences. 

 Its prmcipal aim should be to show what, in the present distribution of plants, may be explained 

 by present climatic conditions and what is a consequetice of former conditions.* 



"By assigning it such a high aim, botanical geography competes with the history of 

 fossil organisms (paleontology) and with geology proper in research on one of the greatest 

 problems of natural science or, rather, of science in general and of all philosophy. This 

 problem is that of the succession of organisms on the globe." 



As an approach to the assigned task, de Candolle, in the early 

 chapters of his book, discusses the effect of external factors— tempera- 

 ture, light, and humidity— on the distribution of plants and also takes 

 up the different types of distribution. The data assembled lead him 

 to the problem of areas of distribution, their character, the changes 

 which they undergo, and the establishment of a number of regularities 

 in the formation of areas. 



This famous work of de Candolle is exceptionally rich in content, 

 and we shall have need to refer to it repeatedly. But here, in our 

 historical review, we must hmit ourselves to this very brief account. 



Somewhat earlier (in 1846) the remarkable work of Forbes, "On 

 the connexion between the distribution of the existing fauna and flora 

 of the British Isles and the geological changes which have affected their 

 area, especially during the epoch of the Northern Drift", opened new 

 vistas for the understanding of the present geographical distribution of 

 plants. As a basis for this work was Lyell's important book, "Prin- 

 ciples of Geology", which first appeared in 1832 and exerted an im- 

 mense influence on the development of biological views, including 

 problems connected with the geographical distribution of organisms. 

 Such influence was furthered not only by the entirely new point of 

 view of the author on the geological past of the earth, but also by the 

 fact that Lyell considered it necessary to include in his work also 

 "phenomena relating to the organic world, which have an equal claim 

 on our attention, if we desire to obtain possession of all the preparatory 

 knowledge respecting the existing course of nature, which may be avail- 

 able in the interpretation of geological monuments" (p. 566). Conse- 



Italics in the original. 



