236 Dr. J. D. Hooker on the Vegetation 



o^ 



is the case with the Fauna, many of the species, and these the most remark- 

 able, are confined to one islet of the group, and often represented in others 

 by similar, but specifically very distinct congeners. 



This examination has led me to take a survey of the vegetation of several 

 other tropical islands, whose plants present much peculiarity, and to trace 

 the effects of isolation in geographical position upon vegetation ; as well as 

 certain characters in some orders, their distribution and proportions, which 

 seem to distinguish insular floras from the continental. 



Before entering upon the details of the vegetation, I siiall shortly allude to 

 the position of the Galapagos, and some of their most important features of 

 climate and soil which afffect the plants, and which I shall extract from the 

 Journals of Mr. Darwin and of other voyagers, including one by the late 

 Mr. T. Edmonstone, hitherto unpublished. 



The Archipelago consists of ten islands situated under the equator, between 

 500 and 600 miles west of the mainland of America at Guayaquil, and the same 

 from the Isthmus of Panama, which lies to the north, and 3000 miles from the 

 nearest of the tropical Pacific islands. The islets are wholly volcanic ; several 

 of the peaks attain a height of 3000 to 4700 feet, some having their flanks 

 studded with innumerable small craters. These are considered to have been 

 formed in the sea, and to be, as compared to the adjoining continent, of recent 

 formation. 



The climate is far from intensely hot, being moderated both by the insularity 

 of their position and the low temperature of the waters of the great south-polar 

 current which washes their shores. The extremes of temperatures observed at 

 different times of day between 9 a.m. and 3 p.m. for thirty-five days in Septem- 

 ber and October include a range of eight degrees only (73° and 65°). These are 

 however, according to Capt. Fitzroy's observations, taken on board ship. The 

 plants on shore are exposed to a much higher and very prejudicial temperature. 

 Thus Mr. Darwin experienced a heat of 93° in his tent, when the thermometer 

 stood at 85° only in the wind and sun, but which, when plunged into the soil, 

 rose at once to 137°, and would have risen higher had the tube been longer. 

 On the other hand, nocturnal radiation does not in all probability reduce the 

 temperature proportionally, the nights being generally misty. The pi-evailing 

 weather is overcast and gloomy, the winds varying for the period alluded to 



