Newcombe, Sensitive Life of Aspürägus ptumosus. 33 



bend, that the bend was promptly straightened out. If geonasty 

 were the effective agent in bending the tip in normal conditions, 

 then it ought not to be so readily overcome on the klinostat by 

 autotropism. 



I see no reason for calling this horizontal bend geonyctonastic, 

 as Czapek 1 ) applies this term to the bending- of the flower stalk 

 of Papaver and Sedum. 



Diageotropism is the cause of the plagiotropic position. The 

 horizontal position is assumed by the tips of seedling shoots kept 

 in the dark from the seed. Revolution on the horizontal klinostat, 

 started while the young shoot is orthotropic, causes the development 

 of the shoot to maturity in the orthotropic condition, with all 

 branches arranged radially and regularly spaced about the central 

 axis. Miss Conover's result by the use of the centrifuge is also 

 significant; since she found that if plants with young orthotropic 

 shoots were kept on the centrifuge for several days, the tips of 

 the shoots finally took a position parallel with the axis of revo- 

 lution, this position corresponding to the plagiogeotropic position. 



Altho the shoot becomes diageotropic on the centrifuge, it 

 remains negatively geotropic on the klinostat, when revolved about 

 its horizontal axis. As already noted, it might be thot that the 

 main axis or its lateral branches would become diageotropic on 

 the klinostat, since they are, or could place themselves by a sniall 

 bend, in the horizontal position, that is, parallel with the axis of 

 the klinostat. That they do not thus develop diageotropism is 

 evidence that the plant must be at rest in order to give gravi- 

 tation an opportunity to act for some time in the same direction 

 on the cells which are active in the process of reversing the 

 response to gravitation. A plant whose aerial shoot is in process 

 of taking the diageotropic position may be reversed so as to place 

 the formerly Upper side downward. The bent portion of the shoot 

 is uninfluenced by this change of 180°. But if the plant is re- 

 volved on the klinostat so that the horizontal axis of revolution 

 passes thru the axis of the bent portion of the shoot, this bent 

 portion being therefore in the horizontal position while revolving, 

 the bent part goes back to the direction of the orthotropic portion 

 of the shoot. This behavior shows again that, altho the cells acted 

 upon by gravitation in bringing in plagiogeotropism may lie with 

 any side directed toward the center of the earth, they must lie 

 in the same position for a considerable time in order to give gra- 

 vitation a footing for action. 



IL The Plagiotropic Shoot remains Radial. 



Since the young shoot of Asparagus, while it is curving from 

 the vertical to the horizontal, and still in a growing condition, 

 may be inverted without changing the progess of the apical portion 



1 ) Czapek, Geotropismus und Pflanzenform - (Wiesners Festschrift, 

 1908. p, 92.) 



Beihefte Bot. Centralbl. Bd. XXXI. Abt. I. Heft 1. 3 



