1X, C,1 Merrill: Plants of Guam 23 
to 1898, at which time Spanish control of the Philippines and 
Guam ceased. For a large part of this period most of the com- 
munication between Guam and the outside world was through 
Manila. From the standpoint of introduced species it is prob- 
ably a period of comparatively few introductions, these mostly 
from Manila, and chiefly ornamental plants with, perhaps, some 
weeds. After the opening of the Suez Canal a considerable 
number of ornamental plants were introduced into the Philip- 
pines from Singapore, including a number of American origin, 
and some of these in turn were introduced into Guam from 
Manila. 
The fourth period is the shortest and dates from the American 
occupation in 1898 to the present time. It has been charac- 
terized mainly by the introduction of economic species, most of 
which have been brought to Guam from the Hawaiian Islands, 
as Guam is a regular stopping place for United States Army 
transports between Honolulu and Manila on the outward, but 
not on the return voyages. 
As already indicated but 61 of the total of 550 species enu- 
merated from Guam, are, so far as is known at present, endemic. 
Somewhat over one-half of the total number of species, 280, or 
51 per cent, are of pantropic distribution, having extended their 
habitat to the tropics of both hemispheres through natural causes, 
or have been purposely or inadvertently transmitted from one 
hemisphere to the other by man. In the case of 55 of those 
pantropic species, including some weeds whose original homes 
have not been determined, and such species of natural distri- 
bution, as aquatics, strand plants, etc., it is impossible to say in 
which hemisphere they may have originated. Of the remainder, 
however, 113 are definitely or fairly definitely of American 
origin, and 112 have probably originated in the eastern hemi- 
sphere. ; 
Considering these 280 pantropic species from the standpoint 
of methods of distribution, about 50 have presumably been dis- 
seminated by natural causes, that is by wind, water, or migratory 
birds; 156, including the cultivated plants, have purposely been 
distributed by man; while about 74, mostly weeds, have been 
inadvertently distributed by man. 
So far as the present vegetation of Guam is concerned, man 
has been an exceedingly important factor in the extension of the 
number of species found in the island. I consider that man, 
with his activities as a disseminator of plants, is responsible for 
the present occurrence in Guam of 314 of the 550 known species ; 
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