326 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



treatment of mechanics. The otherwise expressive q,nd suggestive 

 term growth-vortex may be placed on one side, in that the ex- 

 pression " vortex " has only been used as a geometrical metaphor ; 

 though, on the other hand, it is this vortical condition of growth 

 which is the essential character of a shoot-system, and the term 

 would serve to emphasise the standpoint that a leaf is thus to 

 be regarded as a specialised growth-phase of the parent axis, 

 with which, so long as its primary growth is maintained, it 

 remains co-ordinated, as also with its adjacent members, and 

 within certain limitations under the control of the parent 

 growth-centre. 



