DISTEIBUTION : FUETHEE EESULTS 81 



These results, however, I must beg you to keep to your- 

 jlf, as we are not permitted to communicate Botanical 

 Information (does it deserve the name ?) except through 

 le Lords Commissioners ! 



He perceives also that the distribution and abundance of 

 vegetation in this region depends not on the height of the 

 mean temperature, but on the amount of moisture in the air 

 and the equable level of heat and cold, free from extremes. 



To establish this accurately would prevent critics from 

 repeating that ' nothing of importance had been done towards 

 investigating the causes of difference in Geographical distribu- 

 tion since the publication of Humboldt's work.' 



To his Father 



March 7, 1843. 



I long to see your new work on Ferns ; perhaps you will 

 do something to their Geographical distribution, which seems 

 most dependent on a uniform and moist temperature such 

 as Islands enjoy. All the Magellan species that inhabit 

 the Falklands, there become harsh and coriaceous, from the 

 vicissitudes of temperature, and of the hygrometric state 

 of the air to which they are exposed. . . . The Hygro- 

 meter I consider of more importance than the Barometer 

 in all ordinary cases, that is, where the Islands are not 

 large and the mountains not high. ... I have lately 

 been examining some of my hygrometer observations and 

 find that the difference between the vegetations of the 

 Falklands and the Fuegia may be well accounted for. When 

 the results are placed in a tabular form it is quite surprising 

 to see to what vicissitudes of temperature and moisture the 

 Falkland plants are exposed. Now the mean temperature 

 of the Falklands is the highest, but its plants are exposed 

 to dry winds, great heat of the sun's rays unimpeded by 

 any vapour when it is calm, and great cold at night, whilst 

 those of Fuegia are not so, and enjoy perpetual moisture, 

 and are very sensitive to extremes of temperature, as also 

 to dryness. 



His original intention had been to write a Flora Antarctica, 

 where his work would be on a fairly Httle exploited field. As 



