408 ALPHONSE DE CANDOLLE. 



" The principal facts of geology and palaeontology suffice to explain 

 the facts of botanical geography, or at least to indicate the nature of the 

 explanation, which it requires the progress of many sciences to com- 

 plete. The most numerous, the most important, and often the most 

 anomalous facts in the existing distribution of plants, are explained 

 by the operation of causes anterior to those now in operation, or* by 

 the joint operation of these -and of still more ancient causes, some- 

 times of such as are primitive. The geographical and physical 

 operations of our own epoch play but a secondary part. The only 

 phenomena explainable by existing circumstances are : 1st, the limi- 

 tation of species, and consequently of genera and families, in every 

 country where they now appear ; 2d, the distribution of the individuals 

 of a species in the country it inhabits ; 3d, the geographical origin 

 and extension of cultivated species ; 4th, the naturalization of species 

 and the opposite phenomenon of their increasing rarity ; 5th, the 

 disappearance of species contemporaneous with man. . . . 



" In all this we observe proofs of the greater influence of primitive 

 causes, and of those anterior to our epoch ; but the growing activity 

 of man is daily effacing these, and it is no small advantage of our 

 progressing civilization that it enables us to collect a multitude of 

 facts of which our successors will have no visible and tangible proof." 



De Caudolle did not make the least pretence of attempting to 

 explain the origin of species, but limited himself to the question of 

 distribution. The causes of the present distribution involve ultimately, 

 of course, the question as to their origin, but the immediate question 

 which De Candolle desired to discuss was siuiply, What are the existing 

 facts regarding distribution, and in what direction do those facts point? 

 The Geographie is a storehouse of facts which is still of very great 

 value to students of distribution, and it is to be regarded as a merit 

 of De Candolle's work that he attempted to point out clearly what 

 could be explained by present conditions, as distinguished from the 

 more extended question of what must necessarily be referred to past 

 ages for solution. He, among other points, insisted that in estimating 

 the effect of climate we must consider, not the mean temperatures, but 

 the mean temperatures during the growing season, or those above the 

 freezing point. The question of the origin of cultivated jdants, which 

 formed a part of the Geographie, was again treated in detail by De 

 Candolle in his Origine des Plantes Cultivees, 1883, a work involving 

 not only great botanical knowledge, but also prolonged archaeological 

 study, and which is regarded by experts as a classic on the subject. 



The evolutionary writings of Darwin had their effect on the later 



