PEODUCED BY MAN. 799 



Sachs also has said, such observations and the results deduced from 

 them have a scientific value. As it seems to me, they have not 

 only a scientific value, as all observations which are reducible to 

 weights and measures have, but that they have also a very distinctly 

 appreciable practical value and applicability. 



Anybody who will read the account given by my friend the Rev. 

 Richard Abbay in 'Nature,' May i8, 1876, of the formation of a 

 lake in a district in Australia, 150 miles from Sydney, and 2000' 

 above the level of the sea, subsequently to the destruction of the 

 woodlands round about a particular area of depression, will be con- 

 vinced that this occupation by water of what had been habitable 

 land was not only posterior to, but caused by, the disforesting 

 operations of the various agents specified, namely, squatters, grubs, 

 cattle, sheep, and opossums, not unaided by disease of the trees 

 themselves. The surplus of the water forming the lake corresponds 

 to the enormous quantitative disproportion between the evaporating 

 surface which it exposes when thus collected, and that which it 

 would have exposed when dispersed through all the myriads of 

 leaves which man and his allies had destroyed \ It is not, however, 

 necessary to take such a long voyage as that to Sydney to get an 

 unmistakeable illustration of the evaporating power of leaves. This 

 power can be illustrated e contrario by observing the construction 

 on the treeless Yorkshire or other English wolds of the perennial 

 so-called ' dewponds.' It is not even necessary to travel as far as 

 the nearest down or wold to make this observation, and fill in the 

 necessary details as to extent of feeding ground to catch, and 

 puddled ground to catch, the rainfall. A very simple experiment 

 with plants no farther to fetch than cabbages, will show, as Pro- 

 fessor Wellington Gray tells us (I.e. supra, p. to), that 3000 

 square inches of their succulent leaves will give off as much as a 

 pint of water per diem. 



It may, however, be fairly objected that the rate of evaporation 



n)it den Krankheiten, Je mehi' iiber eine Krankheit geschrieben ist und je melir 

 nach uiid nach sogenannte untriigUche Mittel empfohlen wurden, um so weniger ist 

 sie erkannt. Kaum mochte fiber einen Gegenstand im lebenden Pflanze so viel, und 

 zwar oft einander wideisprechendes, geschrieben worden sein, als liber die Verdun- 

 stung. Wahrend linger, und zwar wobl mit Recht, behauptet, dass eine Wasserflache 

 drei Mai so viel verdunstet, als der Baum, sagt Schleiden, dass umgekehrt dieser drei 

 Mai so viel verdunste als die offene Wasserflache.* 

 ^ See also Ebermayer, 1. c. pp. 184, 185. 



