26 



BRITISH FOREST TREES 



favourable to the development of the different species of 

 forest trees. These normal relative demands on light, 

 dependent on density of the crown foliage and the 

 power of overshadowed twigs to retain life, are everywhere 

 perceptible, but vary with soil and situation, so that no hard 

 and fast classification is possible : concerning the absolute 

 quantity of light requisite for any species we know as little 

 as about the absolute amount of relative warmth. G. Heyer l 

 was the first to classify the forest trees in this respect ; his 

 classification (for central Germany) compared with Gayer's 

 (for southern Germany) is as follows : 



1 G. Heyer, Das Verhalten der Waldbiiume gegen Licht nnd Schalten, 

 1852, p. 3. In the fourth edition of C. Heyer's Waldbau, 1891, p. 41, 

 lime, horse chestnut and sweet chestnut are ranged between hornbeam, 

 and ash and oak, which latter two are placed below maple, sycamore, 

 and elm in the scale. 



