172 MERRILL. 
■ 
Archipelago, having an area of somewhat over 850 square kilo- 
meters. This island is situated off the eastern coast of Luzon, 
in about the same latitude as Manila, the channel separating it 
from Luzon being about 32 kilometers wide in its narrowest 
part; its highest point, Mount Malulud, is about 340 meters 
above sea level. This island was brought under control by the 
Spaniards at an early date, for the town of Polillo was fortified 
for protection against Moro raids in early colonial days. While 
much of its area is covered with virgin forest, still a strip along 
the coast has been cleared and settled, and the island supports 
a population of about 3,000 people. It was presumably inhabited 
before the Spanish conquest. 
In the botanical collections made on this Island by Doctor 
C, B. Robinson, and Mr. R. C. McGregor, in four months, August 
to November, 1909, about 515 species of flowering plants and 
vascular cryptogams are represented,* most of them of wide 
distribution in the Philippines and in the Indo-Malayan region 
generally; but 15 of them being known only from Polillo. In 
studying the Leguminosse of this collection my attention was 
called to the paucity of the unquestionably introduced forms in 
the Polillo flora,'* and an examination of the entire list of species 
collected or observed shows that what was true of the Legumi- 
nosm applies to the other families as well. For instance, of the 
178 species of plants of American origin that are now found 
in and about Manila, and have reached the Philippines since 
the advent of the Spaniards in 1521, but about 25 or 30 have 
reached Polillo, so far as our material shows. Of the 136 in- 
troduced species of presumably oriental origin, apparently not 
more than 35 or 40 are found on the island; and of the 109 
species of cosmopolitan distribution, but whose original homes 
are uncertain, more than one-half of which in all probability 
have been distributed by man, only about 15 are found on Polillo. 
Now the conditions for the growth and reproduction of our 
p numerous introduced species are excellent in Polillo, but from 
our present data regarding the flora of the island, it is estimated 
that less than 100 of the total 457 undoubtedly introduced species 
that are found in and about Manila, have as yet reached that 
island. This is due to the somewhat isolated position of the 
island, and to the comparatively slight communication between 
it and the more densely populated parts of Luzon. The very 
* Robinson, C. B. This Journal 6 (1911) Botany 185-228. 
■ This Journal 5 (1910) Botany 5. 
