230 Auxins in Agriculture 



growth are needed as well. Normally auxin is supplied by the pollen 

 plus some auxin-forming mechanism activated by the pollen; the sub- 

 strates for growth are apparently supplied by mature leaves. The ap- 

 plication of auxin can replace the former requirement, and in some 

 cases at least alleviate the latter. The interesting fact that auxins can 

 alleviate what appear to be limitations in nutrients suggests that auxins 

 may exert their effect in part by bringing about a mobilization of 

 nutrient materials in the flower. 



Although many species of plants have been caused to set fruit par- 

 thenocarpically by auxin sprays, the practice appears to be commer- 

 cially feasible only in tomatoes and figs at the present time. 



