FLORA OF THE GALAPAGOS ISLANDS. 259 



sufficiently explained by tlie relative nearness of the' islands to each 

 other, but it may well be due in part to the circumstance that these 

 insular florulae have in common been protected from much of the change 

 which has, through a sharper competition in the larger flora of the 

 mainland, been forced upon the vegetation of the adjacent parts of the 

 continent. In this matter again insular floras would fare alike, whether 

 the islands they inhabited were the result of emergence or subsidence. 



During the first years, or probably centuries, in the history of islands 

 of emergence their floras, made up as they must be of heterogeneous 

 elements which chance has brought to their shores, would be very unlike 

 the far more homogeneous floras persisting on islands of subsidence ; 

 but after islands of each kind had attained considerable age, — that is 

 an age sufficient to have given rise to a flora as specialized as that which 

 now exists on the Galapagos, it is not likely that their floras would show 

 anj' marked distinction, for, as we have seen, the development would not 

 be unlike in the two cases. Although this negative result is in a way 

 disappointing, it is certainly much better to admit a nullity of botanical 

 evidence in regard to this interesting question than to attribute to the 

 "harmonic '' flora of these islands an historic meaning which it may not 

 possess. 



There is one point, however, from which botanical evidence can be 

 derived which has a certain bearing upon this matter, namely, the 

 relation which the proximity of the different islands bears to likeness in 

 their florulae. The islands are so different in altitude, climate, and 

 consequent fertility, that diversity in their vegetation is by no means 

 surprising ; but the difference certainly reaches a higher degree than we 

 should expect. Thus, the common element between any two of these 

 islands rarely exceeds 75 per cent and is often less than 50 per cent, sink- 

 ing in some cases to nothing. Of course it is not unlikely that these dif- 

 ferences may in some instances be more apparent than real owing to 

 imperfect exploration, and it is probable that further collecting will 

 show at least a small common element between each two of the islands. 

 However, the differences in the recorded floras of the larger repeatedly 

 visited islands cannot be due to our ignorance. Indeed, each new ex- 

 ploration brings quite as much material to demonstrate their diversity 

 as their likeness. The most noteworthy feature of these differences is 

 not, however, their extent, but rather the fact that for the most part 

 they stand in no relation to the distance of the islands from each other 

 or to the depth of the intervening channels. Thus the florulae of 

 Albemarle and Chatham at opposite sides of the archipelago are more 



