646 



P. W. Brian and H. G. Hemming 



the response of sections to GA is necessary before full value can be 

 derived from comparisons of internode sections with similar tissues 

 in their normal anatomical context. 



We have used sections from peas grown in light (green sections), 

 studying their extension in light, because we feel that such a system 

 is closer to conditions in the intact plant than is the more usual sys- 

 tem of etiolated sections growing in darkness, and that more valid 

 comparisons between internode sections and intact plants can there- 

 fore be made. The results now reported supplement those given in 

 an earlier publication (4). 



METHODS 



Unless otherwise stated, sections have been cut from the dwarf 

 pea, 'Meteor.' The procedure used for study of growth of these sec- 

 tions has been described elsewhere (4). One modification of that pro- 

 cedure has been made: 0.75 ml. medium is used for each section instead 

 of 0.5 ml. We have found this to give slightly enhanced extension. 

 Unless otherwise stated, the initial length of sections was 5.1 mm., 

 and growth took place over 24 hrs. at 15° C. in a light intensity of 

 about 800 foot candles. 



RESULTS 



Interaction Between Auxins and Gibberellic Acid 



We have already shown that GA alone has little or no effect on 

 extension of 'Meteor' pea stem sections, but that it ^\•ill induce in- 

 creased extension in the presence of lAA (4). We have since con- 

 firmed this in many experiments. Similar synergism is exhibited be- 



Table 1. Interaction between auxins and gibberellic acid in promotion of exten 

 sion of 'Meteor' pea stem sections. Mean final lengths (mm.) of sections. Basal me 

 dium: 1 per cent sucrose in phosphate buffer. 



Significant dilfcrence between means: 0.36 (P = .05), 0.48 (P = .on, 0.62 (P = .001). 



