Stimulation of Auxin Action by Lipides 429 



in height have been obtained in 2 weeks. Unpublished data show 

 that 14 of 30 surfactants produced the most striking growth promo- 

 tions in our evaluations. These surfactants are distributed through- 

 out the four major classes, namely those of anionic, cationic, nonionic, 

 and ampholytic natures. They also represent a number of the struc- 

 tural subclasses. In nearly all of the surfactants listed, long-chain 

 aliphatic radicals from either acids or alcohols are integral compon- 

 ents. I think this is a fact which we should probably bear in mind 

 when we use any surfactant in our growth regulation studies. 



Dr. Crosby: As we pointed out earlier, we found that the acidic 

 inorganic esters of the long-chain alcohols, the 18-, 20-, and 22-carbon 

 sulfates and phosphates, were all extremely active. We, too, feel that 

 these surface-active effects are extremely important. In regard to Dr. 

 Stowe's work, one brief comment for those who might become inter- 

 ested in working in this area. The compounds which may be pur- 

 chased are all natural products. The benzyl alcohol that we used, 

 and the esters which Dr. Stowe used, are initially impure. I think 

 it is necessary to be sure that a rigorous purification is carried out 

 on all these materials. I also notice that Dr. Stowe observed the same 

 interesting concentration-activity relationships that we did, even 

 though the compounds which he found to be active were as insoluble 

 in the bioassay medium as were ours. I wonder if he would have 

 any comment on how it is possible for there to be such a concentra- 

 tion-activity relationship. 



Dr. Stowe: Well, it's possible, of course, that the concentration 

 here is a bit misleading. These tests were carried out in a standard 

 volume of solution, so we were always adding a known amount of 

 lipide to the bioassay material. I want to emphasize that these are 

 applied as a very good emulsion, and although you cannot, perhaps, 

 speak of a true solution here, specific amounts of the substance were 

 added to each dish, and then you find, as we showed, a nice linear 

 relationship within the right concentration ranges. 



Dr. Vlitos: Your Figure 1 and Tables 2 and 4 showed activity in 

 the pea internode section test with fatty alcohols at different concen- 

 trations, and then Table 3 indicated that lAA was needed in your 

 solutions to show activity. Now I'm not quite clear whether in the 

 first cases you were dealing with endogenous auxins. Would you 

 clear that up for me? 



Dr. Stowe: In every case where you saw an effect, there was also 

 added the optimum concentration of lAA and GA. What we were 

 trying to do was to get maximal growth, and we added everything 

 to the pea sections that we knew would promote growth, and then 

 looked for still other growth-promoting factors. 



