B. P. I.— 804. 



THE EFFECTS OF ARTIFICIAL SHADING ON 

 PLANT GROWTH IN LOUISIANA. 



INTRODUCTION. 



In physiological studies of drought resistance light is a factor which 

 must not be overlooked. The energy received from the sun is largely 

 consumed in transforming water to water vapor, and hence is directly 

 responsible for much of the transpiration from plant surfaces. 



The investigation described in the following pages was carried on 

 in a humid region and was completed before the writer took up l the 

 investigation of light requirement in relation to drought resistance 

 in the semiarid portion of the United States. Nevertheless, since 

 practically the same methods of experimentation have been applied 

 in both regions and since the results obtained in Louisiana have been 

 found to be very useful for comparison with those obtained in Colo- 

 rado, it is deemed advisable to publish the results of the earlier inves- 

 tigation, regarding it as complete in itself but closely related to work 

 which is still in progress. 



The experiments here described were conducted at Baton Rouge, 

 La., during April and May, 1908. The purpose of the experiments 

 was (1) to show the effect of different degrees of shade giving a 

 definite series of light intensities on plant growth and (2) to show to 

 what extent the so-called shade effects were independent of the 

 resulting changes in other physical factors such as temperature and 

 humidity. 



The delay in publication 2 of results has to a certain extent ren- 

 dered them of confirmatory value only, since Lubimenko (1908) 3 

 and Combes (1910) have covered part of the same ground in a very 

 thorough way. Nevertheless, the experiments here described repre- 

 sent a distinct contribution to the subject, since the effects of shading 

 are not the same in different localties, owing to differences in the 

 initial or normal intensity of the light. The results are also of interest 

 as affording indications of the comparative light requirements of a 

 number of species not hitherto included in experiments of this 



1 In cooperation with Dr. L. J. Briggs, of the Office of Biophysical Investigations of the Bureau of 

 Plant Industry. 



2 This delay was due to a desire on the part of the author to repeat the experiments before publication. 

 Since this is now impracticable the results are published in the present form. 



3 All references to literature are indicated in the text by the name of the author and the year of publication. 

 For full citations, see the list at the end of this bulletin. 



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