A STUDY IN ENDEMISM. 299 



account we still have 8 out of 24, or 1 in 3, a higher proportion 

 than occurs among the general Ceylon flora. 



In the plants of the dry zone we had 1 endemic variety in 

 41 or more species ; in the bird-carried things 1 very slightly 

 marked form among 24 species ; in the wind-carried things 2 

 endemic species and 1 variety among 49. 



These facts at once suggest that endemism, other things 

 being equal, goes in general with difficulty of distribution, 

 and with rare arrival in one spot, as has already been hinted 

 at in another paper*. On the top of Ritigala, it being the 

 only high land for a long distance in every direction, birds 

 will naturally settle ; the bird-carried things will in conse- 

 quence tend to arrive more regularly than others. The wind 

 will carry perhaps more species (though if one leave out the 

 ferns, the numbers are approximately the same), but there is 

 no reason why a wind-carried seed or spore should settle on 

 the summit of Ritigala rather than on the plain a few miles 

 away. The average result will thus on the whole perhaps 

 tend to be that except the ferns and the commoner orchids, 

 the wind-carried things will arrive but rarely on the summit of 

 Ritigala. Still more rarely will the plants whose methods of 

 distribution we have classed as doubtful be able to reach the 

 summit. We might thus expect that in families which are 

 reasonably prolific in giving rise to new species, we should 

 find most of these among the doubtful mechanisms, the next 

 among the wind-carried, and the least among the bird -carried, 

 and this is in fact what we do find, the proportions being 1 to 

 3, 3 to 49, and 1 to 24, the last named being only a very slight 

 variety. 



If this be a fair explanation of the facts, we shall expect 

 to find endemism commoner among those things which are 

 rare elsewhere, and in fact we do find- this. Note for instance 

 that the two rare species of Peperomia have both endemic 

 varieties on the top of Ritigala, while the two common ones 



* Willis and Gardiner. The Botany of the Maldive Islands. Ann. 

 Perad. I, 1901, p. 45. 



