Periodical Literature 91 



The instrument measures only diffused light, hence the first 

 inquiry is how much the diffused light radiation amounts of the 

 total light, and its significance. A short chapter reviews light 

 conditions in general. 



In high altitudes the significance of the diffuse light is minimal, 

 hence measurements were made in lower altitudes, where the 

 diffuse light becomes prominent especially on cloudy days ; cloudi- 

 ness also influences color composition of light, so does water vapor 

 influence the intensity. Even with apparently unchanging sky, 

 daylight shows great variation, which does not depend on the posi- 

 tion of the sun. For best residts, in these measurements of light 

 in stands there should be two measvirements made in the open, 

 one before one after, if not simultaneously, and the result percentic- 

 ally related to these. The measurements for good results must 

 be made on cloudless days. 



As regards filtration of light through green leaves, it is mainly 

 the veins which are permeable, the green cell tissues are almost 

 impermeable. The green and yellow parts of the spectnmi are 

 allowed to filter through to a greater degree, while the blue parts 

 are almost entirely absorbed. "Shade" leaves are more permeable 

 than "light" leaves. 



In filtering through crowns, only a small percentage of the light 

 is permitted to pass through; under fir and spruce, only fractions 

 of 1 per cent, filter through without reference to color, while under 

 broad-leaf trees the yellow and green rays 'filter more readily. 

 The small amount which filters is due to the large leaf surface 

 which in a 100-year beech stand is two to three times, and in a 

 55-year spruce stand as much as ten times the area surface. 



The author comes to the conclusion that at least in broadleaf 

 stands for finer investigations the different colors must be measured 

 separately, which is not as necessary with conifers, where therefore 

 simpler methods which measure total light intensity may be used. 



As regards practical deductions the author very modestly points 

 out that these investigations may help to explain why spruce and 

 fir under the cover of even-aged stands regenerate with such 

 difficulty, while in the mixed beech forest, and generally in mixed 

 conifer and broadleaf stands they regenerate readily if the stand is 

 slightly opened, and the yoimg crop maintains itself for decades. 

 The beech stems reflect much light which the conifer boles absorb, 

 besides the broadleaf foliage permits more Hght to filter through. 



