12 TWINING PLANTS. Chap. I 



convex surface ; let the sapling spring up and bend it 

 to the east, and the black line will be seen to run 

 along the lateral face fronting the north ; bend it to 

 the north, the black line will be on the concave 

 surface ; bend it to the west, the line will again be on 

 the lateral face ; and when again bent to the south, 

 the line will be on the original convex surface. JSTow, 

 instead of bending the sapling, let us suppose that the 

 cells along its northern surface from the base to the 

 tip were to grow much more rapidly than on the three 

 other sides, the whole shoot would then necessarily be 

 bowed to the south ; and let the longitudinal growing 

 surface creep round the shoot, deserting by slow degrees 

 the northern side and encroaching on the western side, 

 and so round by the south, by the east, again to the 

 north. In this case the shoot would remain always 

 bowed with the painted line appearing on the several 

 above specified surfaces, and with the point of the 

 shoot successively directed to each point of the 

 compass. In fact, we should have the exact kind of 

 movement performed by the revolving shoots of twining 

 plants.* 



It must not be supposed that the revolving move- 

 ment is as regular as that given in the above illustra- 

 tion ; in very many cases the tip describes an ellipse, 

 even a very narrow ellipse. To recur once again to 



* The view that the revolving H. de Vries ; and the truth of this 



movement or nutation of the stems view is proved by their excellent 



of twining plants is due to growth cbservations. 

 is that advanced by Sachs and 



