378 



SCIENCE. 



[N. S. Vol. XX. No. 507. 



other, this unequal growth being known as 

 epinasty or hyponasty. 



How May Radially Symmetrical Plant 

 Memhers he Placed on the Klinostat to Neu- 

 tralize the Tropic Effect of Gravitation? — For 

 neutralizing the tropic effect of gravitation the 

 horizontal klinostat is always used. There 

 are three positions the plants may occupy as 

 they are fastened to the klinostat. The posi- 

 tions are illustrated by the four diagrammatic 

 figures A, B, C and D. The position in A, in 



D 



which the axis of the plant is made parallel 

 with the axis of rotation, is the one which has 

 been most used in physiological work. The 

 position in B and C is one in which plants 

 have seldom been designedly placed, but in 

 which parts of plants have been generally left 

 without concern if in any way they came into 

 this position. The question now to be con- 

 sidered is this : Are orthotropic parts of plants 

 revolving on the klinostat as indicated in A 

 and B freed from the tropic effect of gravita- 



tion? A consideration of the following re- 

 sults of recent investigation answers this 

 question decisively in the negative. Czapek* 

 found some evidence to show that primary 

 roots, and Miss Pertzf showed that grass stems 

 are not equally stimulated by gravitation at 

 equal distances above and below the horizontal 

 plane. Work done in the botanical laboratory 

 here by Miss Haynes and myself, and soon to 

 be published, demonstrates that both ortho- 

 tropic roots and stems receive their strongest 

 gravitation simulation for bending when 

 those plant members are placed in the hori- 

 zontal position; and that stems are more 

 strongly stimulated to bend when inclined be- 

 low the horizontal than at an equal angle 

 above the horizontal, while roots are more 

 strongly influenced when inclined with their 

 tips above the horizontal than at equal angles 

 below the horizontal. A stem, therefore, in 

 the position shown in Fig. B does not feel the 

 stimulation of gravitation so effectively as 

 in the position 180° removed as in Fig. 0. It 

 is, however, entirely conceivable that the fore- 

 going relations may be true for plants at rest, 

 but may not hold for plants rotating on the 

 klinostat. But numerous tests made by my- 

 self with several species show that both roots 

 and stems rotated on the klinostat in the posi- 

 tion shown in Figs. B and C, or in any oblique 

 position between the horizontal and vertical, 

 bend toward the horizontal as the experiment 

 progresses. Not only then is the oblique in- 

 clination of the plant axis during revolution 

 a faulty one, but the horizontal position as in 

 Fig. A is not proper. In the latter position, 

 it is true, the plant will grow straight, but it 

 will grow straight for the same reason that it 

 grows straight when at rest in the vertical 

 position — because with each deviation from 

 the horizontal position its geotropic response 

 will send it back to the horizontal. 



If one wishes to rotate orthotropic stems 

 and roots on the klinostat so as to free theni 

 from the tropic effect of gravitation there is 

 only one position possible, and that is the 

 vertical position, by which the plant axis dur- 



* Jahri. loiss. Bot., XXVII., 1895, 283. 

 t Annals of Bot, XIII., 1899, G20. 



