EFFECTS OF FOREST YEGETATION ON CLIMATE. 185 



can safely be made strictly applicable to another widely separated 

 from the former. Still, there are certain conditions always capa- 

 ble of entering into the practical working of the problem, such 

 as the effect of forest shade as preventing evaporation — the 

 electrical agency of foliage, so great as to cause a single tree to 

 produce sufficient electricity to charge a Leyden jar — the con- 

 densation of atmospherical vapour, and other agencies, which all 

 belong to the question before us. 



There is also a reciprocal effect of Climate on vegetation, 

 which cannot be omitted, if perfect balancing of elements enter 

 into the problem to be solved. 



And yet we shall find that the Author of the Universe has 

 provided peculiar and wondrous machinery to meet exceptional 

 cases. Take, for instance, the influence of Vegetation on the 

 atmosphere in the case of what a botanist of eminence, and an 

 author of some interesting w^orks on botanical subjects about 

 half a century ago, included in his account of " Eaining Trees." 

 He enumerates the willow and poplar as producing even a gentle 

 shower when grouped together. The properties of such plants 

 as Cormis (onaciola), the Tillandsia, Nejpentlies distillatoria, and 

 other pitcher plants, which are resorted to by monkeys and mice, 

 and especially the " Eose of Jericho " {Anastatica liierochiintind) ^ 

 that extraordinary succulent which inhabits the surface of a 

 burning desert, were experimented upon by the author I refer 

 to, Mr. Murray, F.L.S., who reported on the latter to the Horti- 

 cultural Society of London. 



Mr. Murray refers to a tree met with by Cockburn (" Voy- 

 ages ") at Vera Paz, in South America, which distilled w^ater 

 from the end of every leaf, and in a time of extreme heat 

 had wet ground around it, and names a Calla and an Aga- 

 panthus as affording a counterpart. He further cites Glass's 

 " History of the Canary Islands," as to a tree in the Island of 

 Hierro, called Til by the natives, to which they applied the term 

 garse or sacred, and which had the property of condensing vapour, 

 so that rain, as it were, fell from it so copiously that it was 

 received in a tank and meted out to the inhabitants. 



To justify in some degree this to some apparently incredible 

 fact, Mr. Murray mentions w^hat is capable of more easy verifi- 

 cation, viz., that in avenues of elms and Lombardy poplars, when 

 a fog prevails, though the ground outside the leafy border be dry 

 and parched, within the limits of the foliage it is wet, and he states 

 the time when he noticed this to have been in the month of Sep- 

 tember, 1828, and that the place where this kind of rain fell 

 plentifully from the trees was on the road between Stafford and 

 Lichfield. 



He adds a passage which I will quote entire : — " The great 

 rivers of Europe have their supply in the Glaciers ; but many of 



