FURTHER INVESTIGATIONS ON HELIOTKOI-ISM 105 



unable ID determine accurately. The Sertularia cullival.'d 

 in a dark rcx>m ceased ID grow, though I question \vhet her 

 this was entirely duo to lack of light. 



4. Light (and perhaps gravity) influences not, only the 

 orientation, l>ut also the />ox/7/Vm of the newly formed organs. 

 L have observed, and not in the case of Sertularia only, that 

 the ne\v i>ol//ji-ln'(irin</ branches (tlirays arise from the upper 

 surface of the stem. In Fig. 15, a new stem iS springs from 

 the upper side (the side directed toward the source of light) 

 of the stolon W t . I do not desire to discuss these points 

 more minutely here, as they will form the basis of a paper 

 which is to appear soon, on the form of animals. 



The experiments on Sertularia described here serve only 

 to complete the general consideration of animal heliotropisni 

 and to show more fully the identity of animal and plant 

 heliotropism. The special investigation of the heliotropic 

 behavior of Hydroids is to be the subject of future study. 

 That this is both an interesting and a fruitful h'eld 

 is shown by the beautiful work of Hans Driesch, which has 

 just appeared, on the ''Heliotropism of Hydroids." Driesch 

 arrives at the following result : 



The stolons which are produced instead of polyps under 

 unfavorable conditions iu Sertularella polyzonias, are with the 

 exception of the first, which is turned away from the light from the 

 very beginning, all positively heliotropic at first, becoming 1 nega- 

 tively heliotropic after the growth of the daughter-stolons. They 

 arise from the side of the mother-stolon, which is turned town id 

 the light. (P. 152.; 



This observation of Driesch agrees very well with mine. I 

 shall return to them ill my "Physiological ^Morphology of 

 Animals." 



The results of this studv may be summarized as follows : 



1. Certain sessile animals (Serpulidse, Hydroids) which 

 are compelled to react to light and gravity as radial organ- 



l Zoologische Jahrbllcher, Vol. V. 



