JACQUES LOEB 377 



We can finally submit our idea concerning the nature of the directive 

 effect of gravity upon the arrangement of organs to a quantitative 

 test. When an organ (e.g. a leaf suspended vertically and side wise 



Fig. 3. Same as Fig. 2. Duration of experiment, Oct. 13 to Nov. 1, 1919. 



in^moist air) forms roots or shoots exclusively on the lower side, the 

 material for these new organs must be partly withdrawn from the 

 upper side of the organ and we must be able to prove that the dry 



