Biological Studies on Corymorpha. 413 



tain differences in the stresses when the stem is suspended from 

 one end or the other (Fig. 3). If we assume the axis to be rigid 

 to some extent, then, when the stem is anchored proximally 

 (a and b) its weight may tend to compress its elements in the direc- 

 tion of its axis when it is vertical (a, C); when it is not vertical (b), 

 there may be added to this compression a tension of the elements 

 on the upper side of the stem (Ct), and an increased compression 

 of those on the lower side (Cc). When the stem is hung from its 

 distal end (c and d), a tension may take the place of the com- 

 pression (d, T), and if the stem be not vertical (r), the tension may 

 be increased on its upper side {Tt), a degree of compression added 

 to the tension on its lower side (Tc). There may be, then, a 

 degree of tension on the upper side and a degree of compression on 

 the lower side of each stem; in which case the differences would be 

 differences of degree only. That differences of degree do not 

 modify the reactions of the axial cells is evident when it is remem- 

 bered that a stem hung vertically from its proximal end begins to 

 right itself when, according to the hypothesis, the tension factor is 

 strong on both sides of the stem, and continues in the same direc- 

 tion after it has passed the horizontal, /. e., after the tension has 

 ceased on the lower side and become much reduced on the upper 

 side. 



The inadequacy of the first hypothesis may be shown further, 

 in the discussion of the second. This view was formulated to 

 explain the orientation of free organisms only. It assumes that 

 negatively geotropic organisms tend to move in the direction of 

 greater resistance; being heavier than water, they would meet with 

 greater resistance in going upward than in going downward. 

 "Another stimulus," says Davenport, "which is probably asso- 

 ciated with this, depends upon the fact that an unsymmetrical 

 body, heavier than water, tends to fall with its larger end down." 

 That this view cannot explain the phenomena of orientation in 

 Corymorpha will be clear from the following considerations: 

 First, it presupposes locomotion, while locomotion is not con- 

 cerned in the orientation of Corymorpha. Second, if the stem 

 moves in the direction of greater resistance, a stem hung from its 

 distal end ought to move in the same direction as a stem hung from 



