16 THE DISPERSAL OF PLANTS [pt. i 



by wind, Phragmites and Pennisetum (grasses, ditto), Tourne- 

 fortia and Scaevola (fleshy fruit, bird-carried). In 1897 (34) a 

 further examination showed that there were 50 flowering plants, 

 of which about 30 were due to sea carriage, and 16 to wind. In 

 1905 the number had increased to 137, and the island was be- 

 ginning to show thick forest growth. But again the effect of a 

 barrier should be noted, for the flora of Java alone is over 5000 

 species. 



Thus at first only the regular mechanisms produced any result ; 

 but sooner or later the irregular begin to show, for in the 137 

 are a few species as to whose method of reaching Krakatau it is 

 impossible to do more than guess. On Ritigala, where there are 

 30 species of doubtful method of transport, the time allowed has 

 been enormous, while on Krakatau it was less than thirty years. 

 Yet in those thirty it had, thanks to virgin soil, and somewhat 

 greater nearness to the sources of supply, received many more 

 species than Ritigala. 



Another case of this kind was the re-vegetation of the Taal 

 volcano (38), in the middle of a lake in the Philippine Islands. 

 Here, again, the wind-carried plants arrived very early, and in 

 larger numbers of species, but the bird-carried tended to be 

 numerous in individuals. Both upon Krakatau and upon Taal 

 the vegetation began before very long to settle down into asso- 

 ciations of plants. While at first chiefly herbaceous plants, these 

 were soon followed, as happens in damp regions when sufficient 

 time is allowed, and no other agency, such as man, interferes, by 

 shrub and forest. 



Incidentally, a method of dispersal which has not been men- 

 tioned above must receive a word of notice. This is the explosive 

 mechanism, as it is sometimes called, where, owing to tensions 

 set up in the fruit by turgidity, as in Impatiens, or by drying, 

 as in Claytonia, Montia, Hevea, Hura, etc., the seeds when ripe 

 are jerked away from the plant. The distance is commonly quite 

 small, but when, as in Hura or Hevea, the fruits are at the top 

 of a tall tree may be slightly increased. 



In many respects, the last regular mechanism which has to 

 be mentioned, that of vegetative reproduction by portions of 

 the plant itself, like runners, suckers, bulbils, etc., is the most 

 efficient of all, as witness the profusion of daisies in most lawns, 

 or the difficulty of eradicating Jerusalem artichokes once estab- 

 lished; while anyone who has had the misfortune to have his 

 garden infested with goatweed, enchanter's nightshade, celan- 



