CLIMBING PLANTS. 637 



of movement by which its shoot may sometimes point in one direction, 

 sometimes in another. Bat this is only half the phenomenon, and, if 

 we examine closely, we shall find that the movement is constant and 

 regular, the stem first pointing north, then east, then south, then west, 

 in regular succession, so that its tip is constantly traveling round and 

 round like the hand of a watch, making on an average, in warm 

 August weather, one revolution in two hours. Here, then, is a most 

 curious power possessed by the shoots of twining plants, which is worth 

 inquiring further into, both as regards the way in which the move- 

 ment is produced, and as to how it can be of any service to the plant. 

 Questions are often asked in gardening periodicals as to how hops or 

 other climbing plants always manage to grow precisely in the direc- 

 tion in which they will find a support. This fact has surprised many 

 observers, who have supposed that climbing plants have some occult 

 sense by which they discover the whereabouts of the stick up which 

 they subsequently climb. But there is in reality no kind of mystery 

 in the matter : the growing shoot simply goes swinging round till it 

 meets with a stick, and then it climbs up it. Now, a revolving shoot 

 may be more than two feet long, so that it might be detained in its 

 swinging-round movements by a stick fixed into the ground at a dis- 

 tance of nearly two feet. There would then be a straight bit of stem 

 leading from the roots of the plant, in a straight line to the stick up 

 which it twines, so that an observer who knew nothing of the swing- 

 ing-round movement might be pardoned for supposing that the plant 

 had in some way perceived the stick and grown straight at it. This 

 same power of swinging round slowly comes into play in the very act 

 of climbing up a stick. 



Suppose I take a rope and swing it round my head : that may be 

 taken to represent the revolving of the young hop-shoot. If, now, I 

 allow it to strike against a rod, the end of the rope which projects 

 beyond the rod curls freely round it in a spiral. And this may be 

 taken as a rough representation of what a climbing plant does when it 

 meets a stick placed in its way. That is to say, the part of the shoot 

 w r hich projects beyond the stick continues to curl inward till it comes 

 against the stick ; and, as growth goes on, the piece of stem which is 

 projecting is, of course, all the while getting longer and longer ; and, 

 as it is continually trying to keep up the swinging-round movement, it 

 manages to curl round the stick. But there is a difference between 

 the rope and the plant in this that the rope curls round the stick at 

 the same level as that at which it is swung, so that, if it moves round 

 in an horizontal plane at a uniform height above ground, it will curl 

 round the stick at that level, and thus will not climb up the stick it 

 strikes against, But the climbing plant, although it may swing round 

 when searching for a stick, at a fairly uniform level, yet, when it curls 

 round a stick, does not retain a uniform distance from the ground, but 

 by winding round like a corkscrew it gets higher and higher at each turn. 



