234 



HUTCHINSON'S POPULAR BOTAXY 



study table, and lie watched with interest the long shoot sweeping this 

 grand circle, night and day, in search of some object round which to twine. 

 Ceropegia sandersoni, a closely allied plant (fig. 29G), exhibits the same in- 

 teresting phenomenon. 

 The movement, which 

 has received the name 

 of circumnutation, is, 

 indeed, related to, if 

 not identical with, that 

 which enables a shoot 

 to climb upwards a 

 fact of which it is easy 

 to satisfy oneself by 

 bringing the circumnu- 

 tating shoot of a Hop- 

 plant in contact with 

 any upright object that 

 would serve as a sup- 

 port, when the shoot 

 will at once begin to 

 entwine about it. 

 Kerner suggests that 

 such movements may 

 be caused by the action 

 of co-operating proto- 

 plasts in certain rows 

 of cells on the circum- 

 ference of the shoot; 

 though what it is that 

 impels them to this 

 work he does not pre- 

 tend to say. To him it 

 is ''just as puzzling as 

 the stimulus to the pro- 

 duction of partition- 

 walls in the interior 

 of a cell" and that, 

 as we have shown, is 

 one of the sealed 

 mysteries of biological 

 science. 



We will conclude this chapter with some remarks on the sizes of stems. 

 In prehistoric ages the Animal World had its giants both on land and sea, 

 of which the rocks bear witness in the fossil remains of mastodon and 



IE. Step. 



FIG. 290. WHITE CLEMATIS (Clematis montana). 



The Clematis climbs by twisting its leaf-stalk rccnd acy support that ccmes 



handy. These stalks harden like wire, and are attached to the woody stems Ion? 



after the leaves have fallen. 



