STUDIES IN TOLERANCE OF NEW ENGLAND FOREST TREES 21 



TABLE XIII LIGHT INTENSITIES IN CONTINUOUS SHADE PRODUCED BY CHEESE- 

 CLOTH COVERS ON A CLEAR DAY 



Similar data to that in the last table are displayed in table XIV, 

 except that the readings were taken on a cloudy day between 12:04 

 and 12:26 M. August 14, 1912. 



TABLE XIV LIGHT INTENSITIES IN CONTINUOUS SHADE PRODUCED BY CHEESECLOTH 

 COVERS ON A CLOUDY DAY 



Light Intensities 



A continuous shade of any desired percent of total light, within 

 certain limits, can be maintained during the entire experimental period. 

 In this shade a series of trials was conducted to determine the minimum 

 light intensity at which white pine, balsam fir, and hemlock seedlings 

 could produce starch, the plants being grown under the screens. It 

 was found that when the light intensity was so far reduced as to regis- 

 ter .0266, no starch whatever could be detected in the leaves in the 

 white pine. The hemlock seemed to reach its minimum at about .005. 

 No starch could be found in plants from under two black and four 

 white screens, whereas traces of starch were found in these plants un- 

 der one black and seven white screens with the same light intensity. 

 These trials are being continued using several more varieties. 



It is becoming increasingly evident that the relation of forest tree 

 growth to the light environment can be solved only by carefully planned 

 and executed experiments in the greenhouse and nursery where it is 

 possible, to some extent at least, to control the factors influencing plant 

 growth. We cannot hope that much new information will be obtained 

 concerning this intricate subject by "a study of light in the forest." 



