Chap. I. TWINING PLANTS. 11 



remains straight ; but with twining plants every part 

 of the revolving shoot has its own separate and 

 independent movement. This is easily proved ; for 

 when the lower half or two-thirds of a long revolving 

 shoot is tied to a stick, the upper free part continues 

 steadily revolving. Even if the whole shoot, except 

 an inch or two of the extremity, be tied up, this part, 

 as I have seen in the case of the Hop, Ceropegia, 

 Convolvulus, &c, goes on revolving, but much more 

 slowly ; for the internodes, until they have grown to 

 some little length, always move slowly. If we look to 

 the one, two, or several internodes of a revolving shoot, 

 they will be all seen to be more or less bowed, either 

 during the whole or during a large part of each revolu- 

 tion. Now if a coloured streak be painted (this was 

 done with a large number of twining plants) along, 

 we will say, the convex surface, the streak will after 

 a time (depending on the rate of revolution) be 

 found to be running laterally along one side of the 

 bow, then along the concave side, then laterally on 

 the opposite side, and, lastly, again on the originally 

 convex surface. This clearly proves that during the 

 revolving movement the internodes become bowed 

 in every direction. The movement is, in fact, a con- 

 tinuous self-bowing of the whole shoot, successively 

 directed to all points of the compass ; and has been 

 well designated by Sachs as a revolving nutation. 



As this movement is rather difficult to understand, 

 it will be well to give an illustration. Take a sapling 

 and bend it to the south, and paint a black line on the 



