XXXVl PROCEEDWrGS OF THE 



the intermediate region disappears, the Himalayan chain alone 

 limits the tropical flora, sonl'e of whose types ascend the warmer 

 valleys, whilst a few of the northern ones extend along the mountains 

 of the two great tropical peninsulas. In the extreme east this 

 great mountain -chain disappears or, in receding, turns so far in a 

 northern direction as no longer to oppose a definite impassable barrier 

 running east and west. The climatological results, well explained 

 by Grisebach (vol. i. p. 489 et seq.), come into play, enabling many 

 tropical types freely to intermix with the northern ones, the former 

 prevailing in the south, the latter in the northern portion of the 

 region, but with a gradual, not an abrupt change. 



But with regard to the endemic or widely dissevered highly differ- 

 entiated races (monotypic genera, sections, or very distinct species), 

 Grisebach's views differ widely from those of Asa Gray and other 

 modern naturalists who adopt more or less the theory of evolution. 

 Grisebach, as already observed, entirely ignores community of origin 

 of closely allied or representative species, and is but little disposed to 

 take into consideration ancient dispersion under geological conditions 

 different from the present ones. Each species he believes has arisen 

 — he had formerly said been created, an expression he now abandons 

 in order not to be supposed to prejudge a question which admits of 

 no positive solution — each species has arisen in a particular spot 

 (from what materials he thinks it vain to inquire), under the in- 

 fluence of physical and other external conditions, and has spread 

 ■jiore or less in every direction from this birthplace or centre as 

 far as those external conditions have prevailed, and so far as its 

 progress has been unopposed by insurmountable physical or clima- 

 tological barriers. In conformity with these views he explains 

 closely allied and representative species in a passage which I give at 

 length for fear of misrepresenting him by an abstract. " The birth- 

 place (Entstehungsort) of a plant species," he says, vol. i. p. 515, 

 *' may be taken as the most perfect expression of the concordance 

 between the physical life-conditions of the place and the organiza- 

 tion of the plant ; for this suitability to given influences of inorganic 

 nature gives the highest measure of the capability of preservation 

 which life strives to attain. Upon these propositions is founded the 

 conclusion, that the nearer the centres of different plants are placed 

 geographically, and the less different are therefore their climatolo- 

 gical conditions, the more similar must be their organization, or, 

 what amounts to the same thing, the more species will have arisen 

 in the same genus. This phenomenon is exhibited in all places 

 where we can compare endemic species whose dispersion is limited ; 



