BALL'S FLORA OF THE PERUVIAN ANDES. 387 



the present flora of our temperate zone to a former high- 

 northern vegetation was made clear, and' before the types in 

 question could " with more reason be referred to North 

 America than to Scandinavia." Mr. Ball's remark that, as 

 to many of them, " the balance of evidence points to an 

 original home in the high mountains of lower latitudes " 

 chimes in with his favorite and original doctrine. And this 

 indeed seems likely to gain ground the more it is considered 

 and applied, as he is applying it, to the explanation of actual 

 distribution. 



The interesting problem is to discriminate, as well as may 

 be, the two commingled elements of the northern temperate 

 floras, one of arctic, the other of more endemic mountain 

 origin. An interesting presentation, as concerns central 

 Europe, is made in Heer's " Nival Flora of Switzerland," a 

 posthumous work published by the Societe Helvetique des 

 Sciences Naturelles, of which a summary is given in " Nature " 

 for December 31, 1885. 



The following idea is extremely suggestive. " In a zoo- 

 logical as well as a botanical sense Brazil is one of the most 

 distinct and separate regions of the earth. It is in large 

 part a granitic region, from which vast masses of superincum- 

 bent strata have been denuded, and where the granite itself 

 has undergone a great amount of decay and ablation. We 

 there see the ruins of one of the greatest mountain masses of 

 the earth, where a very ancient flora and fauna were devel- 

 oped, of which portions were able to migrate to a distance, 

 while others have been modified to adapt themselves to the 

 gradual changes of the environment. Many vegetable groups, 

 which are but slightly represented in the higher region of 

 the Andes, such, for instance, as the Ilelastomacem^ probably 

 had their origin in the mountains of ancient Brazil." 



We are now only beginning to reach some conception of 

 the role which the Andes and their prolongation through 

 Mexico have taken in determining the character of no small 

 part of the North American flora. Following up some ideas 

 which were touched upon in this Journal (vol. xxvii., Nov., 

 1884, p. 340) and elsewhere, Mr. Ball writes : — 



