28 
Ridley .— The Distribution of Plants. 
than these plants, viz. Bromeliaceae and Cactaceae. 1 Some at least of the 
species of these orders, notably the Opuntias, introduced into India and 
Africa have thriven remarkably, so that there is no reason to suppose that if 
they ever got across naturally we should not find traces of them, but there 
are none ; the only possible deduction is that these orders were not evolved 
till after the connecting land had disappeared and the Tetraceras, Xylopias, 
&c., and Pothomorphe peltata had been evolved. 
In the same way we may fairly decide that the Pandanaceae absent from 
the New World, though thriving when planted there, were evolved in 
Africa and Asia after the connective bridge was broken, and this is more 
remarkable in that structurally Pandanus appears to have been a very 
primitive plant. It has always struck me as remarkable that this genus of 
maritime and marsh habit, with leaves and fruits that preserve remarkably 
well, has not been found fossil in the European deposits at all. 
Summary of widely distributed Plants. 
I have dealt herein mainly with such widely distributed plants as occur 
in the Malay Peninsula, but this covers really the most widely distributed 
plants in the world of flowering plants. Those that are to be found over 
the large area of the world’s surface fall into four groups: 
1. The weeds, plants which have been accidentally or intentionally 
carried by man to various countries and there, finding suitable soil and 
climatic conditions, have spread themselves widely from the position to 
which they were first introduced. They belong to many different orders, 
but are chiefly herbaceous, and their area of distribution on arriving at their 
new position chiefly depends on their means of dispersion—adhesiveness of 
seeds or fruits, and wind dispersion, being the two most successful methods. 
2. Plants dispersed by sea-currents. These all naturally grow on the 
sea-shore, either in sandy beaches or on tidal mud. The greater number of 
those of the Malay Peninsula cover an area from the Mascarene Islands over 
the Indian Ocean to North Australia and the Polynesian Islands in the Pacific 
Ocean ; a smaller number occur also in South America and West Africa. 
3. A small number of swamp plants, chiefly Cyperaceae, which appear 
to be dispersed by water-fowl, occurring in both hemispheres. 
4. A few which are capable of thriving in temperate and tropical 
regions, such as Phragmites communis and Cynodon dactylon , with a few 
palaearctic forms which have descended along the mountain chains as far 
south as the equator. These latter, illustrated by Sanicula eiiropaea , are 
very scanty in the Malay Peninsula and do not occur in America. They 
are more abundant in Sumatra and Java. 
1 Rhipsalis Cassytlia , Gaertn. (Cactaceae), epiphyte, occurs in Ceylon as well as tropical Africa 
and tropical America. It is the only Cactacea wild in the Old World. 
