CLIMBING-HAIRS 



205 



VIII. SPECIAL .MECHANICAL DEVICES. 



In its widest sense the mechanical system may be held to include 

 a variety of structures, which have indeed no immediate connection 

 with the strengthening of the plant-body as a whole, but which 

 nevertheless perform definite mechanical functions. As a rule the 

 importance of such structures is purely ecological. Many of them 

 find their natural place in the chapter which treats of the motor 



B 



I 



Fig. 76. 



Climbing-hairs of various plants. A. Humulus Lupulus. B. Galium aparine. 

 C. Apioa tuberosa. D. Phaseolus multiflorus. E. Loasa hispida ; in this case the 

 nucleated proximal portion of the protoplast is shut off from the distal portion by 

 a septum. 



system. The present section will be chiefly devoted to structures 

 which serve solely for fixation or attachment. 



Attention may first be directed to the so-called climbing- hairs 

 of twining plauts and climbers in general ; though varying greatly in 

 detail, these hairs are generally arranged so as to prevent the stem 

 from slipping downwards along its support, while offering no obstacle 

 to the upward movement necessitated by longitudinal growth. If the 

 stem of such a plant as Galium aparine, Apios tuberosa, or Humulus 

 Lupulus be stroked between the fingers in the downward direction, 

 no serious opposition is encountered; when, on the other hand, one 



