6 7 6 THE POPULAR SCIENCE MONTHLY. 



We have passed in rapid review the evidence upon which guesses, 

 more or less plausible, as to the age of the world, have been founded. 

 Whatever may be the opinion at which men will ultimately arrive, it 

 cannot but be satisfactory to note from how many quarters and in 

 how many ways Natural Science has in latter days cast light on the 

 inquirer's path. Quarterly Review. 



THE LOCAL DISTRIBUTION OF PLANTS AND THE 

 THEORY OF ADAPTATION. 



By LESTER F. WAED, A. M. 



THERE is one class of facts in the geographical distribution of 

 plants which has not received, at the hands of botanists, the 

 degree of attention which its importance justifies. 



I do not refer to those wide general phenomena which a compari- 

 son of the floras of different countries renders so striking, and by 

 which the more humble and restricted class to which I would call at- 

 tention is usually eclipsed. Such general considerations are, it is 

 true^ exceedingly interesting and important, and are in no danger of 

 receiving too much attention. Nothing could be more absorbing 

 than a close comparative analysis of the vegetation of different hemi- 

 spheres, continents, islands, and zones, of the globe. The most casual 

 survey of such fields reveals marvels, the mere acquaintance with 

 which excites in the mind of the botanist the liveliest interest and 

 pleasure. The strange and leafless euphorbias of South Africa, with 

 their naked, green, parenchymous branches ; the equally singular and 

 grotesque cactuses of America answering to them; the anomalous 

 vegetation of Australia, with its shadeless forests due to their vertical 

 foliage ; the absence of oaks east of the Ural Mountains, and of heaths 

 on this side the Atlantic ; the confinement of the genus Rosa to the 

 northern and of the genus Calceolaria to the southern hemisphere 

 these and numberless other kindred facts connected with the general 

 distribution of plants over the globe are justly calculated to excite 

 the most intense interest, and have given rise to a variety of theories 

 designed to account fpr them. 



The phenomena, however, to which I would more particularly refer, 

 come much nearer home, and may be presumed to have attracted the 

 attention, more or less forcibly, of every one at all conversant with 

 plants. They constitute a distinct class, and may be described in gen- 

 eral terms as facts unfavorable to the received theory of adaptation. 



It has long been regarded as a law of life, applicable alike to animal 

 and vegetable forms, that each species is exactly adapted to the par- 

 ticular habitat where it occurs ; and naturalists, assuming this law, 



