174 
MERRILL. 
phase of the subject has been given considerable attention, com- 
paratively little has been written regarding the origin of various 
pantropic weedy plants that unquestionably have been distributed 
by man. Manifestly the question is a very complicated one, and 
in the case of very many species it is exceedingly doubtful if 
definite proof as to whether certain forms have originated in the 
Tropics of the Eastern or the Western Hemisphere can be com- 
piled. In many cases we can at most indicate that a certain 
species is a native of tropical America, and another a native 
of tropical Asia. 
To illustrate some of the reasons for considering certain species 
as having been introduced, and as natives of the Eastern or of the 
Western Hemisphere, it is well, perhaps, to cite and discuss 
some specific cases, for in a limited space it is impossible to give 
for each species the various reasons for considering it as having 
been introduced, and the reasons why, with a reasonable degree of 
certainty, it may be assumed to be a native of this or that region. 
The evidence from botanical literature is important, but is by 
no means always to be taken as definite proof that a species is 
a native of a certain country. It has not infrequently happened 
that species that are natives of tropical America have first been 
described in botanical literature from material collected in the 
Eastern Hemisphere, this simply showing that such species were 
introduced into India and other countries at an early date in 
colonial history. For example, Waltheria indica L. { = W. ameri- 
cana L.) was first described, in part, from specimens collected 
in Ceylon by Hermann before the year 1679. The species is of 
world-wide distribution in tropical countries, but in looking up 
the generic range it is found that there are approximately 30 
species in the genus, all confined to tropical America, with the 
exception of W. americana L. (W. indica L.). This species in 
the Philippines, and in other countries in the Orient, occurs as a 
weed in the settled areas, and is a manifestly introduced one. All 
evidence points to its American origin, and it can safely be 
assumed to be a native of some part of tropical America. It was 
probably among the first of the numerous species inadvertently 
introduced into the Orient by the early European explorers or 
colonists. 
Sometimes it has happened that a species originating in Amer- 
ica has been described from specimens grown in Asia, but with 
indications as to its origin. For instance Roxburgh® published 
• Plants of the Coast of Coromandel 1 (1795) 67, t. 99. 
