136 



PLANT PHYSIOLOGY AND ECOLOGY 



position is disturbed. Geotropism is equally characteristic of the 

 normal position, since the latter is maintained only in consequence 

 of it. Stems are negatively geotropic, i.e., they grow away from 



y 



Fig. 39. Inflorescence of the fireweed, Chamcenerium angustifolium,show- 

 ins; the movements of the pedicels and the position of bud, flower, and 

 fruit. 



the attraction of gravity. Roots are positively geotropic, i.e., 

 they grow in accordance with the pull of gravity. Leaves of the 

 dorsiventral type place themselves more or less nearly at right 

 angles to the stem and are hence termed diageotropic. In addition 



