302 EDMUND W. SINNOTT AND IRVING W. BAILEY 



Aside from its bearing on the antiquity of oceanic islands and 

 other isolated regions, the present theory as to the origin and dis- 

 persal of herbs is of importance as indicating the conditions under 

 which occurred that momentous botanical event of the Tertiary — 

 the invasion of the Southern Hemisphere by a flood of northern 

 plants. Phytogeography indicates that this invasion took place 

 along three main routes : over the Andes into Patagonia and thence 

 over an extensive antarctic continent or archipelago into New 

 Zealand and southeastern Australia; over the central African 

 highlands into South Africa and Madagascar; and over the Hima- 

 layas and along the East Indies into Australia. These invasions 

 seem to have ceased entirely at the present time, for there are in 

 most cases wide gaps of hundred or even thousands of miles between 

 the northern and the southern ranges of a genus or a species. That 

 the immigration into Africa and Asia ceased some time ago is 

 indicated by the fact that in these continents there are now almost 

 no species identical with northern ones, although the genera are 

 still the same. The highway over the Andes, however, seems to 

 have closed much more recently, for there are a large number of 

 species which traversed it that are still identical with their boreal 

 types. The significant facts in this connection are that, with the 

 exception of a very few genera which are poor in species, this 

 invasion by the "Scandinavian" flora was an invasion of herbs,'' 

 and that herbs are peculiarly adapted to temperate climates. This 

 immediately suggests the conclusion either that these three moun- 

 tain highways were considerably more elevated during the Tertiary, 

 with a consequent increase in the extent of temperate areas (a 



' The presence of such temperate tj^es as Betula, Populus, and Quercus in the 

 Cretaceous of Patagonia, as described by F. Kurtz (" Contribuciones a la palaeophyto- 

 logia Argentina — Sobre la existencia de una Dakota flora en la Patagonia austro- 

 occidental," Revista museo la plata, X [1899], 1902, pp. 43-60) , and in the Cretaceous and 

 even Tertiary of Australia and New Zealand by Baron C. von Ettinghausen ("Tertiary 

 Flora of Australia," Gov. Surv. N.S.W. 1888, p. 82; " Contributions to the Knowledge of 

 the Fossil Flora of New Zealand," Trans. New Zealand Inst., XXIII [1890], 237) 

 (the latter's identifications are often open to grave question, however) has probably 

 nothing to do with the Tertiary invasion of herbs but rather bears witness to the 

 remarkable uniformity and intermingling of the Cretaceous flora. Had these ancient 

 temperate plants been accompanied by anything like the throng of herbs which now 

 surrounds them in the north, it is highly improbable that herbaceous forms would now 

 be so scarce in the south temperate zone. Because of the brevity of their life-cycle, 

 herbs are likely to change very rapidly, and the slight degree in which these "northern" 

 herbs in the antipodes have become altered also bears witness to their comparatively 

 recent arrival. 



