152 ENDEMISM AND DISTRIBUTION: SPECIES [pt. ii 



C. barbatus C. elongatus 



(Bot. Mag. T. 2318) (Fig. in Trimen's Ceylon Flora, 



T. 74) 



Stem cylindrical, tending to quad- Stem quadrangular 



rangular in inflorescence 



Stem pubescent with long hair Stem pubescent with short hair 



Leaves oblong-oval, 1-2 inches Leaves ovate-triangular, 1-2 inches 



Leaves closely pubescent Leaves finely pubescent 



Leaves rather thick Leaves rather thin 



Petioles rather short Rather longer and slenderer 



Inflorescence of condensed cymes, Inflorescence of one-sided cymes, 



each about 5-flowered, forming looking like racemes, about li 



false whorls of 10 flowers at each inches long, one at each side of 



node each node 



Flowers large Flowers small 



Bracts large Bracts small 



Calyx with long hairs Calyx with short hairs 



Calyx of one large ovate upper tooth Calyx of five almost exactly equal 



and four small lower teeth 



Corolla rich purple or white Corolla pale purple 



Grows on rocky places Trails over rocks 



to look at the distribution of the other Ceylon Colei, already- 

 described on p. 54. There is no such difference in the method of 

 dispersal as will account for the great differences in area occupied, 

 nor is there any difference in the other characters of the plants 

 that one can point to, as advantageous or disadvantageous. 



A somewhat larger area than that of Colens elotigatus is that 

 occupied by Campanula Vidalii, which is found (47, p. 427) on 

 rocks near the sea on Flores and two other islands of the Azores. 

 A still more interesting case is Cenchrus insularis, which is found 

 only on one islet of the Alacran reef (75), about thirty miles off 

 the coast of Yucatan, while Cakile alacranensis and Tribulus 

 alacranensis are found on all the four islets of the reef, the largest 

 being less than half a mile long, and very narrow. There seems 

 some reason to imagine that the evolution of these species has 

 been fairly rapid, as they were not noticed by the Admiralty 

 expedition that visited the islands fifty-seven years previously. 

 And scores of similar cases of distribution might be cited. 



We may go on to deal with genera containing several species 

 in the same neighbourhood, all or most of them endemic, gi\'ing 

 a few actual instances. Doona, for exainple, a Ceylon endemic 

 genus of Dipterocarpaceae, has 11 species, whose local distribu- 

 tion (fig. on p. 153) is typical of that of many local genera, or 

 genera with many species (mostly endemic) in one locality. 

 The whole range of the genus (about 4000 square miles in south- 



