6 



BULLETIN 193 



Both hardwoods and softwoods were employed in Knuchel's study 

 of the composition of light in the forests and under single trees. Some 

 of the former consisted of beech, ash, birch and basswood, the latter 

 of spruce, Scotch pine and silver-fir. He set up his spectroscope and 

 made readings in the open. He then moved it into the forest to a 

 previously selected typical or average station and made readings for 

 that forest. Comparisons should enable one to determine the propor- 

 tion of the total rays absorbed by the crowns. The subjoined table is 

 typical, both for forest and single trees. 



TABLE II COMPOSITION OF LIGHT UNDER CROWNS OF BEECH AND SPRUCE 



(KNUCHEL) 



Knuchel finds that the light under the crowns in hardwood forests 

 has a similar composition to that passing through the leaves of the 

 species composing the forest. The exception found was in the pres- 

 ence of blues in the former case. These blues, he says, come through 

 the openings within the crowns. Under softwoods he found no color 

 especially prominent, the light possessing the same composition as the 

 light in the open ; that is to say, no selective absorption was observed. 



The present writer doubts whether valuable data can be obtained 

 by the use of .the spectroscope in the forest. It seems to him quite 

 clear that the selection of a forest station for spectroscopic work which 

 will represent the average of the forest cover and at the same time 

 be as small as the opening which admits light to the spectroscope, is a 

 difficult if not an impossible task. Furthermore the trustworthiness 

 of the comparisons of these light values with the observations made in 

 the open is questionable, since many changes both qualitative and 

 quantitative in character may occur in light values while the instru- 



