FLORA OF THE GALAPAGOS ISLANDS. 259 
sufficiently explained by the 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 
any 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 
‘oem 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 
a3 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 
