420 



B. B. Stoxue 



Table 1 . Comparison of percentage increase in length in 

 24 hrs. of sections from, and of intact zones on, dwarf 'Lax- 

 ton's Progress' peas. Plants and sections continuously exposed 

 to medium by rotating on shaker within petri dishes. Data of 

 two experiments (18), with standard deviations. 



Percentage Increase in Length 



Medium 



II 



10 Mm. Sections 



10 Mm. Zone on Intact Plant 



Basal medium* 

 + GA3 + lAA 



132.4 ± 15.3 

 201.1 ± 14.6 



125.0 ± 16.8 

 234.0 ± 24.1 



* Sucrose, 1.25 per cent + 50 fxM C0CI2 + 5 mM KH2PO4 



(pH 5.5). 



Figure 1 shows the data obtained both with the dwarf 'Laxton's 

 Progress' pea and the 'Alaska' pea. In each case, section elongation 

 can nearly be doubled by an extract of pea glycerides or with pure 

 methyl esters of certain fatty acids. The Tween detergents, which 

 are also fatty acid esters, also showed growth-promoting activity. It 

 is apparent that the differences between the dwarf and the 'Alaska' 

 pea sections are small. In fact, although dwarf pea sections have 

 been used predominantly in this work, each time results have been 

 checked on 'Alaska' pea sections the response has been very similar. 



When the new lipide factor is added to the tests of Table 1, using 

 one of the most active compounds, methyl linoleate at 68 |.u\/, the 

 section growth is increased to 113.8 ± 7.3 in the first test and 107.4 

 ±: 9.7 in the other. Even so, these increments still bring growth up to 

 only four-fifths of that of untreated plants and to not quite half the 

 growth anticipated in the presence of GA;;. 



In the hope that some other li})ide might futhcr stimulate the 

 growth response of the sections, some thirty-odd pure substances 

 have been examined. Table 2 summarizes these results, which indi- 

 cate that many alkyl compounds with a chain length greater than 

 twelve carbon atoms are capable of accentuating the growth of pea 



