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22 The Philippine Journal of Science 1914 
by its aboriginal inhabitants who introduced the economic plants, 
such as yams, breadfruit, bananas, coconut, certain aroids, rice, 
etc., that were found by the Europeans to be generally distrib- 
uted in Polynesia. In the comparatively slight intercommuni- 
cation between Guam and other islands during this period, 
doubtless many of the weeds of general Indo-Polynesian distrib- 
ution which have originated in the Old World were introduced. 
The second period is relatively much shorter and extends 
from the discovery of Guam by Magellan in 1521 to some years 
after the discontinuance of the Acapulco-Manila galleons in 
1815. The plants introduced during this period were mainly 
of American origin, including such economic species as the 
sweet potato, maize, tobacco, tomato, cacao, maguey, chico, pine- 
apple, arrow-root, custard apple, peanut, cassava, papaya, pep- 
pers, and various other plants of value for food, fibers, medicine, 
and ornamental purposes. At the same time a great many 
weeds of American origin were introduced including a few that 
are to-day found nowhere outside of tropical America except in 
Guam, and still others that outside of tropical America are 
known only from Guam and the Philippines. During this in- 
terval of about three hundred years Guam was in regular com- 
munication with Mexico, as for most of the period there was an 
annual ship between Acapulco and Manila via Guam. On the 
return voyage, however, the ships took a northern route and 
did not touch at this port. Ships from Manila to Guam were 
apparently dispatched at very irregular intervals. Undoubt- 
edly some, perhaps many, of the weeds of oriental origin 
were introduced into Guam from the Philippines during this 
period, for such economic plants as the mango, tamarind, coffee, 
santol, some of the citrus fruits, the pomegranate, nipa palm, and 
various ornamental plants were introduced from Manila by the 
Spaniards. 
The last ‘‘nao,” as the Acapulco-Manila galleons were called, 
was dispatched from Manila in 1811 and from Acapulco in 1815. 
These were government ships, but after 1815, when they were 
definitely discontinued, commerce was opened to private individ- 
uals and the ports of San Blas, Mexico; Guayaquil, Ecuador; and 
Callao, Peru, were opened to the Manila trade. There is no 
doubt that Guam still continued to be a port of call for the west- 
bound ships from the above ports. However about 1824, with 
the independence of the Spanish colonies in America, this com- 
merce practically ceased. 
The third period is still shorter and extends from about 1815 
