THE STEM 



41. Tendrils ol the Pas- 

 siini Flower. 



tendril is known by its position. A tendril from the axil 

 of a leaf, like that of the Passion Flower (Fig. 41), is, of 

 course, a stem, i.e. a 

 In'anch. 



80. In the young- 

 stage, wlien still ex- 

 tended, tendrils are 

 endowed witli motion 

 and with sensitive- 

 ness to contact. 

 Their movements are 

 like those of twining 

 stems, — tliey de- 

 scribe circles or el- 

 lipses until brought 

 against some object. 



When, by the curving of the ti[), a hold has been secured 

 upon this object, the tendril coils in a double spiral. 

 The coil or spiral itself is of importance in all such 

 cases, for its elasticity prevents a sudden stress caused, 

 for example, by a bla.st of wind, from snapping the 

 tendril off, as might be the result were the tendril 

 straight and already tiglitly drawn at the moment of 

 onslaught. 



" I have more tliaii once gone on purpose, during a gale, to watch a 

 Bryony growing in an exposed hedge, witli its tendrils attached to the 

 surrounding bushes ; and as the tliick and thin branches were tossed 

 to and fro by the wind, the tendrils, had they not been excessively 

 elastic, would instanth' have been torn olf and the plant thrown pro.s- 

 trate. But as it was, the Bryony safely rode out the gale, like a ship 

 with two ancliors down, and with a long range of cable ahead to serve 

 as a spring as she surges to the storm." — D.\rwix. 



81. The tendrils of the Passion Flower are wonderfully sensitive to 

 sliglit pressure. In Darwin's experiments, "A bit of platinum wire, .'(, 

 of a grain in weight, gently placed on the concave point, caused a 

 tendril to become hooked, as did a loop of soft, thin cotton thread J^ 

 of a grain. The point of a tendril of Pas.tiflora gracilis began to move 

 distinctly in twenty five seconds after a touch, and in many cases after 

 thirty seconds." 



