Growth Substances 



389 



a period of minimum stem growth, but once they are laid down, stem 

 growth again accelerates. Compensatory correlations (p. 98) of various 

 sorts also have their basis in auxin action. Removal of the root tip almost 

 always stimulates growth of lateral roots below it, somewhat as in 



Fig. 18-13. Relation of presence of achenes to growth of strawberry. All achenes 

 have been removed early in development except three vertical rows ( left ) or three 

 horizontal ones (right). Growth of the receptacle is limited to the region in contact 

 with the achenes. ( From Nitsch. ) 



Mar., 1950] 



30 



25 



20 



15 



10 



DIAME TER 

 IN MM. 



I 

 2 



O o- — o o o 



le 



is 



18 



21 



25 



DAYS AFTER POLLINATION 

 Fig. 18-14. Auxin and growth of the straw- 

 berry. Curve 1, control. Curve 2, growth of 

 fruit from which all achenes were removed 

 and auxin in lanolin paste substituted. Curve 

 3, like 2 but without the auxin. (From 

 Nitsch. ) 



Fig. 18-15. Effect of 2,4-D on 

 leaf shape. Below, leaf of un- 

 treated plant of Pisum sativum. 

 Above, plant treated with 2,4-D 

 paste. ( From Wenck. ) 



