282 



BOTANY 



PART I 



of themselves to maintain mi erect position. The erect stems of other 

 plants, which often secure their own rigidity only through great 

 expenditure of assimilated material (in xylem and sclerenchyma) are 

 made use of by stem-climbers as supports, on which to spread out their 

 assimilatory organs in the free air and light. The utilisation of a 

 support produced by the assimilatory activity of other plants is a 

 peculiarity they possess in common with other climbers, such as 

 tendril- and root-climbers. Unlike them, however, the stem- 

 climhers accomplish their purpose, not through the use of lateral 

 clinging organs, but by the capacity of their main stems to twine 

 about a support. The first internodes of young stem-climbers, as 



Ki;. -_7. The movements by which alflow-r <it Ai-imittnit iiii/llns nonius its proi-i po.Mtion when 

 the axis bearing it (S)is inverted. I, Inverted position ; II, position resulting from gi-otrnpisni. 

 the flower facing the parent axis; ///, flower .again facing outwards. aftT thf exotropic 

 movement. 



a rule, stand erect. By further growth the free end curves 

 energetically to one side, and assumes a diageotropic, more or less 

 oblique or horizontal position. At the same time the inclined apex 

 begins to revolve in a circle either to the right or to the left. This 

 is the movement which it has been customary to speak of as 

 " revolving nutation," but which it is better to term REVOLVING 

 MOVEMENT. The expression " nutation " is not in this case correct, as 

 by it are understood autonomic movements ; while THE REVOLVING 



MOVEMENTS OF STEM-CLIMBERS RESULT FROM THE EXTERNAL 



STIMULUS OF GEOTROPISM, which causes a promotion of growth in 

 either the right or left side of the young internodes of the inclined 

 shoot apex. As a result of this, a movement towards the other side 

 is induced. On account of the direct connection of the apex of the 

 shoot with the lower erect internodes, this revolving movement 

 necessarily gives rise to a similar rotation of the revolving apex on its 



