SPECTRUM, HELIOTROPIC REACTIONS 



29 



an additional difficulty, in this way: that if by chance one 

 polyp is directed to the light and there are only five polyps on 

 the stem it may appear as if 20 per cent of the polyps had reacted 

 positively, while in reality the stem was not influenced by light 

 at all. To avoid misinterpretations of this kind from influencing 

 the interpretation of results we always give the number of 

 polyps in a stem in the following tables. 



In indicating the wave length it should always be remembered 

 that the region given is usually the center of a small zone which 

 contained the stem; since the latter is not straight and since 

 the polyps are irregular in position it is not possible to indicate 

 the position by one line in the spectrum. 



We will now enumerate some experiments. In the first verti- 

 cal column is given the wave length, in Angstrom units, to which 

 the stems were exposed (indicating in the next column the color 

 of the region). In the third column we give the fraction of the 

 number of polyps bending to the source of light over the total 

 number of polyps. In the fourth column we give the percentage 

 of the polyps bending to the light. Each experiment was made 

 with different material on different days, unless the contrary 

 is stated (table 2) . 



From this experiment we may deduce, first, that for this dur- 

 ation of exposure (five minutes) the rays to 5700 A.u. (i.e., the 



TABLE 2 



Experiment 1: Exposure of Eudendritim polyps for five minutes to the 



spectrum 



