IV] TREES AND LIGHT 47 



Foresters are accustomed to term the Birch and Larch 

 and similar trees "light-demanding" as contrasted with 

 the "shade-enduring" Beech, Yew, &c., and they arrange 

 ordinary forest trees in some such category as the following. 

 Generally speaking it is found that the Larch, Scots 

 Pine, Birch and Aspen demand more light than the other 

 pines, the Maple, Sycamore, Oak, Ash, Chestnut, Elm, 

 Alder and Willows ; and that the Spruce, Silver Fir, 

 Hornbeam, Beech and Yew are capable of enduring more 

 and more shade. 



It must be carefully understood, however, that no 

 single species is absolutely fixed in such a category as 

 the above : differences in age, vigour, situation and soil, 

 latitude and altitude, &c., all have their effects in enabling 

 any particular tree to withstand shade better or worse 

 than usual. All we can say is that, other conditions being 

 equal, the species at the head of the list require freer 

 exposure to the light of the particular locality than do 

 those towards the bottom of the list, and care must be 

 taken in planting such species in mutual proximity that 

 light- demanding trees are not dominated by shade- 

 enduring species. 



Moreover, we must not forget that a tree is a sensitive 

 organism, and may be exposed to too intense as well as to 

 too feeble a light for health. 



There are a series of phenomena, as yet but partially 

 and vaguely understood and regarding which our ignorance 

 is expressed in the term correlations, which nevertheless 

 play important parts in the shaping of trees. 



If two long shoots of a Willow are cut and hung up, 

 one so that its basal end is uppermost, the other in the 

 normal position, both in moist air and similarly treated in 

 every respect other than position, new shoots arise at the 

 end nearest the tip and roots at the basal end in both 



