CH. II] INTO NEW AREAS 15 



a long period of drought, but Ritigala is high enough and steep 

 enough to condense the moisture of this wind, and its upper part 

 therefore forms an outher of the wet zone. Upon the summit is 

 a wet-zone flora, which must in general have reached it by over- 

 steppmg the whole 40 miles of separation, for the configuration 

 of the country, and the course of the monsoons, render it very 

 improbable that the intermediate country can ever have been 

 "wet," i.e. have received rain in the south-west monsoon also 

 which alone would render life possible for these species. Of the 

 103 wet-zone plants at the summit, 24 had fruits suited to bird 

 carriage, 49 had light fruits, seeds, or spores suited to wind, and 

 30 may be classed as doubtful, being entirely unsuited to any 

 of these methods, and yet equally so to growth in the inter- 

 mediate "dry " country. Here, therefore, was carriage by doubt- 

 ful methods over a good 40 miles, most probably bv the aid of 

 birds in some way, as the species were largely mountain species. 

 Of the actual Avind-carried species, 24 were ferns and lycopods 

 with dust-like spores, 20 were orchids with very light seeds, and 

 the other 5 were Compositae, Apocynaceae, and Asclepiadaceae, 

 with parachute-like fruit or seed. 



It is noteworthy that the peak of Ritigala, a mere small area 

 projecting out of a sea of dry-zone plants, was probably not a 

 virgin area, though suitable to wet-zone forms. It was probably 

 covered with plants of "dry-zone" type, M-hich have only gradu- 

 ally been ousted by "wet-zone" arrivals, and in the whole of 

 the enormous period since it became suitable to the latter it has 

 only received 103 of them, and also bears a great number of 

 plants which are the same as those of the dry-zone areas below. 

 The Maldive Islands, which were probably a virgin area, have 

 received 160 species, in probably much less time, and Krakatau, 

 which we shall next consider, received 137 in thirty years. 



Krakatau. the classical instance of the distribution of plants 

 to new ground, is an island in the strait between Java and 

 Sumatra, about 25 miles from each, and about Uh from the 

 nearest island with vegetation. In 1883 it was "absolutely 

 sterilised by the famous eruption. In 1886 Dr Treub of Buiten- 

 zorg vi.silud it to see to what extent it had been re-coloniscd (109); 

 he found many blue-green Algae, 11 ferns (spores easily carried 

 by wind), 9 flowering plants on the beach (carried by currents, 

 or drifted over by wind), and 8 inland, two of these the same as 

 on the beach. These eight were a Wedelia, two Comjzas, and a 

 Senecio, all Compositae, with dandelion-like fruits, easily carried 



