Bird. — Lianes of the Ancient Forest of Cwnterhury Plains. 339 



they attain a length of 9-11 cm. If in this downward curvature a tendril 

 comes into contact with some suitable support it encircles the latter, 

 and, being thus held firmly in position, the rest of the tendril con- 

 tracts into a double spiral (fig. 8). But in the absence of a support a 

 tendril coils into a continuous spiral, and after remaining for a time in 

 this posit'on it again straightens, and later shrivels up. In tendrils 

 which have obtained a hold on some support the part which is actually 

 in contact with the latter becomes greatly thickened, often attaining a 



Pig. 8. — TetrajMthaea australis. Young shoot, with tenckils. 

 Fia. 9. — Tetrapathaea australis. Tendril, showing thickening. 



diameter fully twice that of the rest of the tendril (fig. 9). By the develop- 

 ment of mechanical tissue these tendrils persist for a great length of time, 

 being common on stems which have grown to 6 cm. in diameter. At 

 this age they are still extremely tough, being able to withstand a tension 

 of 3 kg. These old tendrils are usually almost straight, and thus it is 

 evident that, other things being equal, a younger tendril which is spirally 

 coiled will be able to withstand a still greater strain. 



As tendrils are present upon a plant in large numbers, and as they are 

 widely distributed, the plant, in growing upwards to new positions of sup- 

 port, is admirably adapted for withstanding all strains — vertical strains due 



