258 Forestry Qtiarterly. 



light gains its great significance from the fact that it is the only 

 manageable factor of them all — it is the lever with which all 

 others are set in operation. The effect of light depends on its 

 kind, intensity, and direction of its working. As to kind, we 

 distinguish direct and diffuse light. Direct light is chiefly valu- 

 able in the formation of leaf and flower buds, hastening develop- 

 ment of leaves and producing a more vigorous, plentiful leafage. 

 That too strong direct light may be harmful is shown by the pres- 

 ence of protective devices in exposed plants. Diffused light is 

 the more important in general growth of plants. However, it is 

 not so much the kind but the intensity of light that is important. 

 Each species — each plant — has an optimum — a definite sum to- 

 tal — of temperature and light supply, in which it thrives, varying 

 with latitude, altitude, soil, age, and development of plant, etc. 

 In regard to light this optimum, while difficult to determine, lies 

 in the upper half of total useful light supply. There is more 

 danger in overshading than overlighting for all species, though 

 not in equal measure. 



The direction of light rays influences its form building power. 

 We distinguish outer, inner and floor light. Outer light is direct, 

 diffused or mixed light, striking the outside crown. Inner light 

 is all light of value inside the crown. It is chiefly diffuse. Its 

 intensity is important in bole cleaning or the formation of inner 

 leaves. Floor light is that which reaches the soil through the 

 crown cover. It is very important in operations concerned with 

 care of soil, reproduction, etc. Its intensity depends on species, 

 being in inverse ratio to crown density, and is indicated by the 

 condition of the soil flora. 



We recognize that light exerts a profound effect on increment. 



Diameter increment is in direct ratio to light supply. But for 

 height increment the influence varies with the species. Mono- 

 podially crowned species, like larch, spruce, fir are stimulated by 

 open position. The opposite is true for species inclined to spread- 

 ing crown, as the broadleaved, and pine. Yet with pine, there 

 may be exceptions, as is shown by the latest records of Saxon 

 experiment stations, where 40 year pine, with wider spacing, 

 showed increase of mean height. Also, Schwappach found on an 

 experimental area opened up freely according to Wagener's pre- 

 scription that well lighted stands from 30 to 45 years, i. e. within 



