CLIMBING PLANTS. 127 



either throughout their whole diameter, or on one 

 side alone ; they subsequently become stronger and 

 more woody, sometimes to a wonderful degree ; 

 and in some cases they acquire an internal struc- 

 ture like that of the stem or axis." l 



In one species of Tropceolum examined by Dar- 

 win the first young leaves were like tendrils, with- 

 out anything resembling a leaf-blade. As the 

 plant grew older it produced these tendril-like 

 filaments with enlarged tips, then with partly 

 formed blades, and finally with perfect leaves. 

 The filaments, as well as the perfect leaves, were 

 very sensitive, and they moved spontaneously and 

 contracted spirally, as do perfect tendrils. The 

 plant would be called a tendril-bearer if it acted 

 in this way when mature ; but when full-grown it 

 is a true leaf-climber. This shows us very plainly 

 that tendrils are modified leaf-stalks. They may 

 also be formed from modified branches or flower- 

 stalks. 



Plants with tendrils are wonderfully interesting 

 in their perfect adaptation for purposes of climb- 

 ing. The tendrils sweep round and round, and 

 when they come in contact with a support, their 

 sensitiveness to pressure makes them bend towards 



.! " Climbing Plants/' p. 81. 



