836 



THE NATURE BOOK 



THE I'OTKNTIl.l.AS COVER IN A LARGE AREA 

 BY .'\1EANS OF THEIR CREEPING STEMS. 



travels, reaching out farther and farther 

 ever}^ time the circle is complete. On 

 a warm day the stem of the Bean goes 

 round at a wonderfully rapid rate. In 

 one case the tip of the shoot traversed a 

 circumference of two feet in a couple of 

 hours, showing that the rate was an inch 

 in five minutes — no mean performance 

 for a plant. 



When the circumnutation of the Bean 

 has been fully observed, it is instructive 

 to place a support within reach of the 

 shoot. This should be upright, seeing 

 that as a general rule the twining 

 plants are not able to climb save 

 up a nearly perpendicular object. 

 The attachment to the stick is 

 a matter which is very quickly 

 accomplished, for a few minutes 

 after the shoot is actually touch- 

 ing the tip commences to curl 

 round. As soon as the hold is 

 securely accomplished, the manner 

 of growth changes into the spiral 

 twining by means of which the 

 stem will advance up the support. 

 This is probably related to, if 

 not identical with, the process 

 of circumnutation. The passage 

 (jf the bean-shoot up the support 

 is now very rapid, and on a close 



summer's night will be as much as two 

 inches in the twelve hours. 



Next in importance to the twining 

 plants are those which clamber up by 

 means of tendrils. These organs are 

 among some of the most wonderful in 

 the plant world. One interesting British 

 l^lant producing tendrils is the White 

 Bryony, a common hedgerow species. In 

 this case the climbing organs are large, 

 sometimes being as much as four or five 

 inches in length. The means by wliich 

 the tendrils secure a hold, and then twist 

 themselves into the permanent position, 

 offers a peculiarly fascinating study. 

 Prior to their attachment to any object, 

 the processes maintain a curious swaying 

 movement, which must increase the 

 probability of their coming into contact 

 with a support. Directly the tip of the 

 tendril is within reach of some object it 

 begins to entwine itself without delay. 

 In the space of a few minutes, supposing 

 the conditions to be favourable to rapid 

 growth, the slender thread has started to 

 encircle the support. The underlying 

 cause seems to be partly in the stimulating 

 influence induced by the hght rubbing 

 of the under side of the tendril against 

 the object. When the tendril is at its 

 greatest period of activity it may be 

 induced to curl round almost any object 

 which is offered to it. 



A pencil, or the little finger, passed 

 gently along the inner side of the organ 

 will cause it to twine around the support ; 

 the shght rubbing making the movement 

 a good deal more ra])i(l than is normally 



THE NASTURTIUM CLIMBS BY MEANS OF ITS 

 LEAF-STALKS. 



