FOREST DEMANDS 35 



Light. Light is absolutely necessary to the growth of 

 trees. The result of closing the stomata the breathing- 

 pores of the leaves which an absence of light brings about, 

 is elsewhere shown (page 70). But all trees are not alike 

 in the amount of light they require to maintain a fairly 

 vigorous growth. All will do best by having a proper 

 amount, but some demand more than others ; or, to state it in 

 another way, some can endure more shade than others. Those 

 which can endure the most shade are termed " tolerant," 

 in contradistinction to those which can endure little or none, 

 and the latter are designated " intolerant." The need of 

 light which some species manifest has greater significance 

 when natural regeneration is depended upon than when a 

 forest is established by sowing seeds or setting out trees. 

 In the former many trees, whether tolerant or otherwise, 

 may be driven out because the rapidly growing ones will 

 suppress them with their shade ; and the fact that nearly all 

 of the most valuable timber trees are light-demanding makes 

 this possibility a feature which should not be overlooked. 

 Most of the Oaks, the Pines, Spruces, Hickories, Elms, 

 Ashes, Cherry, Basswood, Yellow Poplar, Larches, Chest- 

 nut, and several others are more or less intolerant, while Sugar 

 Maple, Beech, Hemlock, and a few others are more or less 

 tolerant, and will thrive, after a fashion, in the shade of 

 their own or other species. Hemlock will grow under a white 

 pine, but a white pine will not thrive and reach a full 

 growth in the deep shade of any tree. It can be easily deter- 

 mined whether a tree is intolerant of shade even when grow- 

 ing in the open. If the small twigs and limbs, which at 

 first grow next to the stem and large limbs, are dead or 

 dying, and the leaves of the tree are mainly on the outer 

 surface of the crown, or none of moment next the large 

 limbs, the tree may be set down as intolerant to a great de- 

 gree. Some trees, as Maple and Beech, may have nearly 

 the whole top a quite dense mass of small limbs and twigs 

 bearing leaves, while a White Ash, Cherry, or other intoler- 

 ant tree will have the interior of its crown open and the 



