STUDIES IN TOLERANCE OF NEW ENGLAND FOREST TREES 7 



ment is being moved to a new location and adjusted. Knuchel points 

 out somewhat in detail this possibility of error. 



In the solution of the problem of forest succession, little is gained 

 by showing that the weakened light which passes through the sun leaf 

 is comparatively rich in yellow and green rays, unless it is shown ex- 

 perimentally that this light is able to decompose carbon dioxid and 

 otherwise influence the development of the seedlings of the future for- 

 est. Our knowledge of the value of the different rays of light in the 

 development of plants is so rudimentary that great care should be used 

 in drawing general conclusions in view of the lack of experimental 

 data. 



Further and valuable observations have been made by other work- 

 ers in this field who have attempted to discover the amount of light 

 actually passing through the leaves unabsorbed, and, finally, to deter- 

 mine the ability of such light to decompose carbon dioxid. For ex- 

 ample Linsbauer (11) has determined the amounts of light which pass 

 through sun and shade leaves of the same species and through sun 

 leaves of different species. His results indicate that more light passes 

 through the shade leaves than the sun leaves of the same species, but 

 that the intensities are greatly reduced as shown by the following 

 table, which represents only a small part of his data. 



TABLE HI AMOUNT OF LIGHT PASSING UNABSORBED THROUGH LEAVES 



(LINSBAUER) 



He found that the amount of light passing unabsorbed through sun 

 leaves varies with different species from .006 to .0003, totality equall- 

 ing 1,-and that in the case of shade leaves the figures varied from .003 

 to .02. For a given tree with both sun and shade leaves, the amount of 

 light passing through the leaf unabsorbed decreased from the center of 

 the crown toward the periphery. If the leaves of the tree were formed 

 to use the greatest possible amount of total light available, exactly the 

 opposite result would be expected. Only in the case of Quercus 

 Robur did the sun leaves allow more light to pass through unab- 

 sorbed than did the shade leaves. 



