208 MERRILL. 
* 
Malay Archipelago, 789 to tropical Asia, 425 to tropical Aus- 
tralia, 424 to tropical America, 402 to tropical Africa, and 355 
to Polynesia. Only 124 are endemic, including the locally intro- 
duced and cultivated species. 
8. Species that are cosmopolitan in the tropics, at least those 
that are found in some parts of both hemispheres, aggregate 
424, of the total of 1,007 considered. About 90 of these are 
considered to have spread from one hemisphere to the other 
through natural causes, although in about one-half of these cases 
the species may have been transmitted by man. As to the Phil- 
ippines, 334 of these pantropic species have been introduced 
by one means or another, about 242 purposely, and about 92 
inadvertently. 
9. As to the origin of these pantropic species, 177 are consid- 
ered to have originated in tropical America, and 138 in the 
tropics of the Eastern Hemisphere. In the case of 109 species 
it has been impossible definitely to determine where they may 
have originated. 
10. Pantropic weeds of American origin are more dominant 
and more numerous in species and in individuals in the Phil- 
ippines, than are those of oriental origin. This is probably due 
to fundamental differences in aboriginal floristic conditions. In 
some parts of tropical America, at least in the drier regions, 
open treeless or partly treeless regions have probably existed 
from the earliest times, thus permitting the development of a 
flora consisting of annual, or of small, perennial, light-loving 
plants. In the Philippines, the Malayan region generally, and 
perhaps in large parts of tropical continental Asia, the high 
and continuous humidity has tended to the development of con- 
tinuous forests, and hence, as to the herbs and small shrubs, 
the development of a shade-loving flora. The destruction of 
forests over large areas has provided the habitats for light- 
loving species, an element lacking or but poorly developed in 
the original flora, thus permitting the growth and rapid disse- 
mination of plants adapted to these conditions when once intro- 
duced. 
11. Among the introduced element in and about Manila, more 
than 70 per cent of the species flower continuously, or practically 
continuously, during all months of the year. Of the indigenous 
species but about 8 per cent flower continuously, over 90 per 
cent having restricted periods of anthesis. 
Vol VII, No. 2, including pages ^7 to lUy was issued July 1, 1912, 
