142 



JOUKNAL, R.A.S. (CEYLON). 



[Vol. IX, 



are foreigners, and by far the greater number are from the 

 New World, and therefore comparatively lately introduced, 

 i.e. within the last three centuries. 



This invasion of the Eastern Tropics by an army of 

 herbaceous or half-shrubby weeds from the W. Indies is a 

 remarkable fact.* It has had the effect of causing a very 

 uniform character in the vegetation of the cultivated coast 

 regions of the whole tropical belt, and it would not now be 

 possible in many cases to even guess the origin of many 

 species from their present distribution ; generally, however, 

 their origin and history can be traced without much 

 difficulty through the botanical treatises of the 16th and 

 17th centuries. f 



Some of these plants, however, appear to inhabit naturally 

 all the three tropical areas of Africa, Asia, and America, 

 these are mostly such as are capable of having been trans- 

 ported by ordinary natural means of dispersion in past times. 



3. In temperate zones the opposite state of things has 

 held good, and the interchange of such plants between 

 Europe and N. America has been all in favour of the Old 

 World. English weeds have largely established themselves 

 in the United States, &c, whilst few, very few N. American 

 ones have succeeded in getting a permanent footing in 

 Europe, those which have done so being a few annual 

 species exceptionally provided with means for copious dis- 

 persion of seed, or aquatics. The same readily colonizing 

 English weeds have also spread themselves over the cool 

 mountain districts of the East, and as regards Ceylon a 

 fair proportion of our introduced plants belong to this 

 category. These, of course, are found chiefly about 



* It is the clearing of land for cultivation that gives these alien 

 plants their opportunity. A country naturally covered with forest has 

 no native species able to compete with these foreign inhabitants of open 

 country and plains, which, when once introduced, are thus able to 

 spread without hindrance. 



f The rapidity with which some useful or ornamental species were 

 transported from the New World to the Old is very striking. The 

 Portuguese came first to Java in 1496, four years after the discovery of 

 America ; and in 1520 Magellan sailed direct from S. America to the 

 Philippines. It was from these islands that the other Eastern tropics 

 obtained many of the American plants now so abundant. 



