CHAPTER III 



THE INTRODUCTION AND SPREAD OF 

 FOREIGN SPECIES 



One of the most commonly misunderstood or misinterpreted 

 phenomena in connection with the distribution of plants is that 

 exhibited by many species that have been introduced, whether 

 intentionally or not, into countries to which they were not really 

 native. Often they have spread rapidly, and are now among the 

 most common plants. The casual traveller in Ceylon, for example, 

 will notice everywhere by the roadside the sensitive plant 

 (Mimosa), the Mexican sunflower {Tithonia), Lantana, Mikania. 

 various Cassias, guavas, Turnera, Vinca rosea, etc., not one of 

 which is really native. Higher in the hills he will see abundance 

 of clover, dandelion, gorse, shepherd's purse, spurrey, etc., also 

 introduced in recent times. 



When Europeans first settled in tropical and other countries 

 to which they were newcomers, the places in which they located 

 themselves were not determined by mere chance, but were 

 places to and from which transjiort was most easily and cheaply 

 obtainable (114, p. 36). They had not come to these countries for 

 the benefit of the inhabitants, but to begin trade with Europe 

 in those products that they only could supply. Accordingly the 

 white men settled at the mouths of the great rivers like the 

 Ganges, Yang-tze-kiang, Amazon, de la Plata, etc., where ports 

 existed or could be easily made, and goods could be easily 

 brought down from inland. E\'en more frequently they settled 

 upon the islands, beginning with the smaller ones. Here there 

 was less risk of invasion by the natives in great force, and trans- 

 port from the interior was usually easy, by reason of the com- 

 paratively small size of the country, though of course river- 

 mouths were utilised, for purposes of port accommodation, and 

 of transport from the interior, \vhenever possible. 



In these places introduced plants were soon foimd spreading 

 about, especially when the country, prior to occupation — as was 

 very often the case, especially on the islands — Avas in its natural 

 state of forest. No notice was taken of this spread until the rise 

 of the theory of Natural Selection, when it was found that these 

 introductions apparently gave good evidence in its support. This 



