422 B. B. Stoiue 



Table 2. Comparison of effectiveness of different classes of simple alkyl lipides in 

 enhancing auxin-induced growth of 'Laxton's Progress' pea epicotyl sections. Full 

 details are published elsewhere (18); the most active compounds are cited in text. 



Alkyl Lipide Class 



Compounds less than C12. 

 Fatty acid methyl esters. . 

 Triglycerides 



Fatty alcohols 



Monoglycerides 



Free fatty acids 



Efficacy 



Many esters, glycerides, alcohols tested; none active. 



All 9 tested (in C12 to C20 range) found active. 



All 4 tested (tri-palmitin, -stearin, -olein, and -linolein) 

 active. 



4 (in C18 to C22 range) active, 2 (Cu and Cie) inactive. 



2 (C16 and Cig) active, 4 (Cu, Cig, C20, and C22) inactive. 



All 7 tested (in C12 to C22 range) found inactive. 



sections. The free fatty acids are ineffective, despite the fact that 

 their esters are among the most active compounds. The most active 

 simple alkyl substances discovered to date are triolein, trilinolein, 

 methyl mynstate, and selachyl alcohol. All are of comparable ac- 

 tivity, but none can bring section growth entirely back to normal — 

 values like those reported above for methyl linoleate being typical 

 of the group as a whole. 



Thus it is likely that yet other factors are required for optimal 

 growth, and in particular for the growth promotion caused by gib- 

 berellic acid. Lockhart's (13) and Galston and Warburg's (9) results 

 may also be interpreted as indicating that the rest of the plant pro- 

 duces a factor which enhances gibberellin action on the sections. 

 Nonetheless, attempts to extract such an additional factor have not 

 been successful. It seems likely that the inissing substance could be 

 the caulocaline postulated some years ago by \Vent (24). It was de- 

 duced that this was synthesized in the roots and could only travel 

 through living tissue. Went showed that it recjuired pea tip auxin, 

 but pea tips are now known also to produce gibberellin (13). 



Alternatively, it may be that gibberellic acid and dihydrogib- 

 berellic acid are not the active form of gibberellin but are converted 

 to it in some other part of the plant. This would fit in ^\'ith the 

 results of Phinney (15) reported at this conference, which indicate a 

 biochemical pathway of gibberellin synthesis in maize. 



Since in this study a technique had been adopted Avhich made it 

 possible to prepare stable aqueous emulsions of nearly any fat-soluble 

 substance (18), it was thought desirable to investigate the effect of 

 the hitherto inaccessible fat-soluble vitamins on the section bioassay. 

 Tests of vitamins A, Do, E, K^, and (3-carotene revealed that of these 

 E and K, were as effective as the simple alkyl lipide comj)ounds cited 



