552 



PLANT GROWTH AND PLANT COMMUNITIES 



Chemical control of leaf expansion 



I propose to start with some results from the doctoral thesis of 

 J. K. Templeton, who, during the course of his study of the physio- 

 logical action of the phytotoxic compound 3-phenyl-l,l-dimethylurea, 

 investigated the possible competitive effects of chemically allied com- 

 povmds, including 1,3-diphenylurea, which contemporaneously Shantz 

 and Steward ( 1955 ) were isolating as an active component of the 

 coconut milk factor. It was found that when the diphenylurea was 

 added to the external solution in which S. natans was growing, there 

 was for a time an increase both in the mean leaf area and the length of 

 the internodes ( FigurelG ) . 



More recently a number of other compounds have been tested, 

 alone and in combination, and some selected results are given in Figure 

 17. It is evident that 3-indolylacetic acid and gibberellic acid inhibit 

 rather than promote leaf expansion, while 2,3,5-triiodobenzoic acid 

 causes a small increase in area. In passing, it should be noted that at 

 similar levels of concentration TIBA increases venation in L. minor 

 ( Sargent and Wangermann, 1959 ) . 



As a final example, some effects of kinetin ( 6-furf urylamino pu- 

 rine) are given in Table IV. The induced changes in leaf area are 

 clearly linked with the stage of development. For the first pair of 



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Figure 16. The influence of 1,3-diphenylurea on the area per leaf and the 

 internode length of Salvinia natans. 



