XIV] AMOUNTS OF WATER TRANSPIRED 141 



Von Hohnel, who estimated that the proportion of water 

 transpired in equal times by the same dry weight of leaf 

 substance was on the average as follows : 



Ash 85,614 



Birch 81,433 



Beech 74,858 



Hornbeam 72,973 



Elm 66,170 



Sycamore ... ... 58,595 



Oak 54,572 



Norway Maple ... 53,063 



Spruce 13,501 



Scots Pine 9,426 



Silver Fir 7,178 



Black Pine 6,734. 



Whence we see that the Pines, Spruce and Silver Fir 

 transpire very much less water than any deciduous tree 

 examined. As the result of prolonged investigations it 

 was concluded that where the water-supply is sparse, the 

 Conifers transpire about one-tenth as much as do the de- 

 ciduous Dicotyledons, but where there is plenty of water 

 the proportion may rise to one-sixth or one-seventh as 

 much. 



Now it is interesting to note that there is one Conifer, 

 viz. the Larch also with narrow leaves, which for a 

 time may transpire as vigorously as do the most active of 

 the Dicotyledons referred to, e.g. the Ash (which, with the 

 Birch, Lime, Alder and Pyrus torminalis, is one of the 

 most powerfully transpiring trees in Europe), and at first 

 sight it appears as if we had here a serious contradiction, 

 for the Larch is an Alpine Conifer of the highest altitudes. 

 Such is not the case, however. The Larch simply faces 

 the conditions with a different equipment of adaptation : 

 its narrow and delicate leaves are deciduous, and are 



