RELATION TO LIGHT. 35 



Fir, Silver Fir, and Scots Pine have the deepest roots, and 

 therefore need a deep soil for healthy growth ; while Aspen, 

 Birch, Willow, Poplar, and Spruce have only a shallow root- 

 system, but also grow better in a deep than in a shallow soil. 

 Beech, Ash, Elm, Maple, Sycamore, Hornbeam, White Alder, 

 Oak, Austrian Pine, and Larch thrive on limy soil ; but much 

 lime acts injuriously on Sweet- Chestnut, Douglas Fir, and 

 Maritime Pine. Humus or leaf-mould improves all kinds of 

 soil; hence replantation on true "woodland soil" is usually 

 more successful than the first planting of waste lands and poor 

 pastures, in which there is probably a deficiency of nitrogen in 

 an easily available form. 



(3) As regards light and shade, trees are classifiable as light- 

 demanding and shade-enduring, according to the amount and 

 the intensity of sunlight needed for the assimilation of carbon 

 and the elaboration of the sap the demand being apparent 

 from the amount of foliage borne by the tree-crown (which, 

 of course, varies with the situation and the quality of the 

 soil). The light-demanding trees most intolerant of shade are 

 Larch, Birch, and Robinia ; Pines, Poplars, and Willows ; Oak, 

 Ash, Elm, and Chestnut; less intolerant of shade are Alder, 

 Lime, Horse-Chestnut, Maple, and Sycamore ; while Beech and 

 Hornbeam, and most evergreen Firs and Cypresses (especially 

 Spruce, Douglas and Silver Firs, and Red Cedar) are shade- 

 enduring, as also the stool-shoots of the kinds of trees usually 

 grown as underwood in copses. All our woodland trees thrive 

 best with their crown of foliage freely exposed to sunlight ; but 

 Beech and Silver Fir seedlings need protection against scorching 

 and frost for the first two or three to four or five years, and are 

 therefore usually naturally regenerated under parent standard 

 trees. But the poorer the soil, the greater is the demand for 

 liirht, and the less the tolerance of shade. Young Sycamore 

 and Ash springing up self-sown can tolerate heavy shade at 

 first. In trees the capacity for tolerating shade is shown by 



