CLIMBING PLANTS. 



123 



of dots along the upper side of the outstretched 

 revolving end of such a stem (Fig. 34), and to note 

 that when it has moved round a quarter of a circle 

 these dots will be on one side, when half round 



the dots occupy the lower side, 

 and when the revolution is com- 

 pleted they are again on the 

 upper side. That is, the stem 

 revolves by bowing itself over to 

 one side; is either pulled over, 

 or pushed over, or both, by some 

 internal force, which acts in turn 

 all round the stem in the direc- 

 tion in which it sweeps ; and so 

 the stem makes -its circuits with- 

 out twisting." : " The first pur- 

 pose of the spontaneous revolving movement, or, 



1 " The phenomenon finds its explanation in the fact that first one 

 and then another side of the organ elongates more rapidly than the 

 rest. If this takes place alternately on two opposite sides, the apex 

 therefore bends over at one time to the left, at another to the right ; but 

 if at the circumference of the organ different sides in succession gradu- 

 ally take their turns in the process, then the pendent apex must rotate 

 in space." Sachs, "Lectures on the Physiology of Plants," p. 546. 



FIG. 34. MORNING- 

 GLORY. 



