IX, C, 1 Merrill: Plants of Guam 25 
glandulosa Merr., Sida glomerata Cav., and Mitracarpum hirtum 
DC. (also in the Society Islands). It is not at all strange, when 
we consider the old Acapulco-Guam-Manila trade-route, that we 
should find in Guam to-day certain American weeds that did not 
reach the Philippines, or if they did that they have not persisted 
here, such as Sida glomerata, Mitracarpum hirtum (also in the 
Society Islands), and Ammannia coccinea. Mitracarpum, a 
genus confined to America, was extended to Guam by the de- 
scription of Mitracarpum torresianum Cham. & Schlecht., which 
is a synonym of M. hirtum DC.; the occurrence of a species of 
Mitracarpum in Guam was doubted by K. Schumann & Lau- 
terbach,® who surmised that the Guam record was due to 
a mixture of labels. That the species was actually collected in 
Guam by Chamisso cannot be doubted, for it still persists there 
and is represented in our recent collections from the island. 
K. Schumann* had previously recorded it from the Society 
Islands. ' 
In connection with a general discussion of the vegetation in 
and about Manila in Luzon‘ I have already considered at length 
the question of those plants of pantropic distribution and its 
significance. In considering only those plants found in and 
about Manila it was found that out of a total of 1,007 species no 
less than 425 were of greater or less distribution in the tropics 
of both the eastern and western hemispheres. I came to the 
conclusion that of these 425 species of pantropic plants but about | 
90 were distributed from one hemisphere to the other by natural 
agencies; that about 242 were purposely transmitted and that 
92 were accidentally distributed by man. As to origins, so far 
as this matter could be determined at the time, 177 were con- 
sidered to have originated in tropical America, 138 in the tropics 
of the Old World, and 109 were considered doubtful as to origin, 
including the 90 species of presumably natural distribution and 
certain weeds and weed-like plants regarding whose native coun- 
tries I could arrive at no definite conclusion. Very many of 
these weeds or weed-like plants, now of wide tropical distribu- 
tion, have certainly been transmitted from one hemisphere to the 
other by man, but are now so ubiquitous that it is difficult or 
impossible, from their present distribution, definitely to deter- 
mine of which hemisphere they are natives. The list includes 
°F]. Deutsch. Schutzgeb. Siidsee (1901) 589. 
*Engl. & Prantl Nat. Pflanzenfam. 4* (1891) 146. 
' Philip. Journ. Sci. 7 (1912) Bot. 145-208. 
