414 Forestry Quarterly 



that the record we get on photographic paper will give us a notion 

 as to the relative intensity of the photosynthetic rays even though 

 the other set of rays are the ones that are actually measured. 



One of the first attempts to measure separately the different 

 rays of the solar spectrum was made in 1907 by Zederbauer, of 

 the Austrian Forest Experiment Station at Mariabrunn. His 

 theory was to measure the quality of light as well as the quantity, 

 since a forest cover affects the light that penetrates it and trees 

 are known to have the power of selective absorption. It is known 

 also that intolerant trees use mainly the red rays and that tolerant 

 trees use principally the blue to violet rays of the spectrum. 

 These notions led to the invention of Zederbauer's spectrophotom- 

 eter, and instrument which records the rays of varying length of 

 which sunlight is composed. This is a complicated instrimient, 

 unsuited for field use. There is no instrument for measvuing the 

 quality of light in the field. For field use, the Clements photom- 

 eter, even though it does not take into account the quality of 

 light, is so far the best instrument we have. 



Probably the most recent investigations upon light determina- 

 tions are those of Knuchel. In an article (80) which appeared 

 in 1914 in the Proceedings of the Central Forest Experiment 

 Station of Switzerland he not only summarizes the work done in 

 that field, but gives us some new ideas concerning the quality and 

 the quantity of light in the forest, especially as it is affected by 

 the crown cover. By means of an instrimient devised by himself 

 he measures the vertically incident diffused light and he shows of 

 what importance this is to plant life. The work by Knuchel is 

 probably the last word in light investigations and is worthy of 

 more discussion than it is possible to give here. 



The Application of Modern Forest Ecology to Silviculture 



Before 1870, silviculture received its first scientific treatment 

 at the hands of the old masters and their contemporaries. Not 

 long after modern forest ecology was founded it began to exert 

 its influence upon silvicultural thought and practice. The in- 

 vestigative attitude began to pervade every phase of the art and 

 the experiment stations began to throw light upon many problems 

 which the practitioner had been unable to solve. The works on 

 general silvicidture pubhshed between 1880 and 1885 by Gayer, 

 Wagener, Borggreve, and others show the results of this new atti- 



