240 THE POPULAR SCIENCE MONTHLY. 



tribute itself in. groups ordered according to the latitude ; and this 

 movement once started, the differences between the groups be- 

 came continually more accentuated by the increasing exclusion 

 in each of them of a part of the types which they originally con- 

 tained. There resulted from this a constant impoverishment of 

 northern countries as comj)ared with southern ones, which gained, 

 at least by contrast, what the former never ceased to lose. The 

 movement has thus tended to a differentiation by zones, and has 

 resulted in despoiling them, but in unequal proportions, increas- 

 ingly as they are removed from the tropical zone, the only one 

 which has been exempt from the spoliation. 



Let us not forget that, parallel with this movement, working, 

 moreover, with an extreme slowness and in harmony with it, an- 

 other movement, purely organic and evolutionary, although in- 

 cited, if not directed, by the former, has not ceased to push to de- 

 velopment and to morphological differentiation various groups of 

 plants ; particularly of those which, relatively young and plastic, 

 were susceptible, by this fact, of giving birth to new forms, and, 

 by successive splittings, to new types. These are the angiosperms, 

 which, having once gained preponderance, have offered the spec- 

 tacle of an increasing multiplicity of races and forms. That mul- 

 tiplicity could only increase. The displacements resulting from 

 the climatic depressions have aided in it by inducing changes of 

 stations and opening new cantonments to races not yet fully 

 established. The revolutions of the surface, continental contigui- 

 ties, and the more or less accentuated orographic relief, have con- 

 stituted other factors not less active in the general push of species, 

 incessantly solicited to vary as they adapted themselves to the 

 soil of the regions into which they penetrated, as they scattered, 

 and as they struggled victoriously against rival species. 



Such is the spectacle which the vegetation of the globe has not 

 ceased to present ; and the existing forests appear as the final re- 

 sultant and ultimate consequence of that long series of alterna- 

 tives which is summarized in the expression, " the struggle for 

 existence." — Translated for the Popular Science Montlihj from the 

 Revue des Deux Mondes. 



The development of a new vegetation on Krakatoa is affording a rare oppor- 

 tunity for studying the origin of floras. The old vegetation was totally destroyed, 

 with all its seeds, by the great heat that prevailed during the eruption, and the 

 island was covered with a thick layer of cinders and pumice-stone. But in June, 

 1886, a new growth, of ferns and isolated plants of phanerogams, had appeared on 

 the shore and the mountain. The riddle of its appearance in a soil apparently so un- 

 promising was explained, on examination, by finding that the mineral had received 

 a coating of fresh-water algse, which gave it a gelatinous and hydroscopic quality, 

 by virtue of which a higher vegetation could gain a standing. The phanerogamic 

 plants are similar to those which take possession of newly-raised coral islands. 



