1913. 



PUBLIC DOCUMENT — No. 31. 



65 



Summary Tabic. 

 [Measurements in centimeters.] 



It will be noticed that the difference in development of the 

 plants in the preceding- experiments arises from the fact that 

 they were growing under varying light intensities. Many phys- 

 iologists, particularly Wiesner, have studied the effects of light 

 intensities on the conformation of plants, and it. is necessary, 

 therefore, to mention only in a general way the modifications 

 caused by light. Altogether too few plants were used to elimi- 

 nate the differences arising from individual variation ; never- 

 theless, the summary table shows a more or less uniform 

 variation in the development of the plants due to different light 

 intensities. 



Xo. 5N, which was growing in the greenhouse, was taken as 

 a normal for growth comparison. The light conditions for this 

 ])lant were taken as 100 per cent., and represent those character- 

 istic of our latitude at the time the experiments were made, 

 minus an average loss of about 18 per cent, from the greenhouse 

 glass. ]^o. 4, which was screened, received only 74 per cent. ; 

 No. 3, 48 per cent. ; No. 2, 2G per cent, and No. 1, 24 per cent. 

 These percentages, of course, are purely relative, and are based 

 on the assumption that the plants under normal conditions in 

 the greenhouse received 100 per cent, of light. It will be ob- 

 served that most of the injury occurred to those plants growing 

 under the poorest light conditions, and the least where the light 

 conditions were best. In considering the results as given in 

 the summary table, which are more reliable than those in the 

 other tal)les, as they represent averages, much difference is 

 shown in the development. The greatest average height of the 



