220 



exposition of whose theory has induced a better comprehension and a modification of 

 existing methods of management. 



It is a known fact, that the higher the organization of a plant the more light is needed 

 for its proper growth with few exceptions, such as some cryptogamia and mosses, which 

 require direct light. Most of the mosses prosper with a small amount of light under the 

 shade of trees, and disappear when the forest in its more advanced age grows thinner. 

 The contradiction to this rule presented by the vegetation in mountainous regions is only 

 an apparent one, because there the frequent mists replace the shade of forest trees. 



The most highly organised plants exist in that part of the globe, where the sunlight 

 is most intense and the farther we go from the equator towards the poles, the more- 

 increases the proportion of cryptogamia to phanerogamia. 



Now the quantity of sunlight necessary for the development of the most highly or- 

 ganised plants, the Cotyledons, is very different for difierent species and genera. Many 

 plants of this group can only live in the shade of forest trees, like the Asperula mono- 

 tropa, and disappear with the removal of the forest. So do the forest trees themselves 

 evince a difference of requirements with regard to light and shade, and on these different 

 requirements are based many important forestal operations. 



All forest trees may be classified into three groups, which, however, gradually run 

 into each other, and express the relative position of each species with regard to its need 

 of light or shade. We may call these groups the shade-loving, shade-bearing, and light- 

 needing. Criteria for the classification of the different species into these groups are given 

 in the appearance of the foliage, its greater or lesser density, in the capacity of over- 

 shadowed branches and trunks to sustain life and to withstand the shading out by the 

 domineering neighbours, and in the power of young seedlings to prosper in the shade of 

 their mother trees. 



In judging of the foliage of a species, such specimens as have grown in the full enjoy- 

 ment of sunlight, ought not to be chosen as samples, because this full enjoyment of light 

 tends to enlarge the amount of foliage and so to form a denser crown ; it is only in the 

 forest that the characteristic appearance of foliage belonging to each species can be 

 discerned. 



Those species which form dense crowns, evidently need less light than those with 

 higher foliage, for, as the interior leaves of the former get less light, and yet vegetate, it. 

 is evident that they need less for their existence. Yet though some species, like the fir, 

 are so tenacious that for sixty or more years they will preserve life under the dense shade 

 of the overshadowing forest, there is no doubt that all species, after a certain period of 

 life, prosper best and increase in the greatest ratio when in the full enjoyment of light, 

 because light favours the production of a large number of leaves, which in their turn excite 

 greater activity in the processes of life or growth of the plant. 



This effect of the sunlight is probably not so much due to its luminous quality as to its 

 temperature, which incites evaporation through the leaves, and with it circulation of the 

 sap. 



It is natural that species with a dense foliage i.e. with a large leaf area, tend at the 

 same temperature to evaporate more water than those with lighter foliage, and therefore 

 draw more heavily on the moisture of the soil than the latter, or we may say on the same 

 soil, under the same conditions, the trees with light foliage will longer withstand the drying 

 effect of the hot sun, than those with dense foliage. This influence of the sun, inducing 

 increased evaporation, tells, especially in young plants, where the i-oot.s are drawing their 

 supply of water from a confined area, and the foliage does not stand in a favourable pro- 

 portion to that area. In this period of life, it is of the utmost importance to the forester 

 to understand this interrelation of sunlight, foliage, and humidity of soil to shape his 

 operations accordingly. 



The writer is as yet not sufl&ciently conversant with the requirements in that respect 

 of the species, which forms the forests of North America, to be able to attempt the esta- 

 blishment of a scale, denoting the relative capacity of the species to sustain shade or tiieir 

 comparative demand for light. 



In Germany, where we have only fifteen or sixteen species, that may be considered 

 worthy of notice in the realm of forestry, Dr. Heyer established the following scale, in which 



