170 MERRILL. 
countries, and especially with tropical America, a great impetus 
was given to the dissemination of plants, and the flora of this 
Archipelago, like that of many other regions has been greatly 
enriched by species introduced within historical times. While 
many of the introduced forms have proved to be of the greatest 
economic importance, still many undesirable citizens were repre- 
sented among the numerous aliens. With the advent of the 
Spaniards came a considerable number of European species, both 
weeds and plants of economic value, and very many forms from 
other parts of the Orient, A very large number were introduced 
from tropical America through the medium of the galleons 
on the old Acapulco-Manila trade route, which will later be 
given a more detailed consideration. 
The Philippine Archipelago, as geologists reckon time, is of 
comparatively recent formation, and the logical conclusion re- 
garding the origin of its flora is that the original vegetation 
of the group, like its human inhabitants, reached the Archi- 
pelago from older neighboring countries of the Indo-Malayan 
region. Much of this original vegetation may have reached 
the group through previously existing land connections, but 
ocean currents, winds, migratory birds, and lastly, and perhaps 
not least, man must be considered, for species have been intro- 
duced by all these factors, and all have hence had their influence 
on the present character of the rich and varied flora. It is 
not my intention at this time to discuss the probable origins 
of the flora as a whole, it being primarily the same as that 
of the Malay Archipelago. We have, however, in the high lands 
of northern Luzon a very pronounced continental, that is, Asiatic 
element, where the Himalayan types are more numerous than 
in any other part of the Malay Archipelago; there is also a 
decided Polynesian, and a decided Australian element in the 
flora, and I have previously advanced the theory^ that our dom- 
inant Malayan element has been introduced chiefly from south- 
eastern Malaya, rather than from western Malaya, that is, the 
Malay Peninsula and the Sunda Islands. 
Whatever may have been the geological history of the Archi- 
pelago, and whatever the source of its flora, it is manifest from 
a study of the present flora that the Islands as such have been 
separated from neighboring countries for a very long period 
of time, sufficient, in fact, to develop a very marked endemism. 
While the percentage of endemism as to genera is comparatively 
a 
Ann. Jard. Bot. Buitenz. Suppl. 3 (1909) 277-306. 
