J. VAN OVERBEEK 239 



on leafy cuttings. Next it was found that ammonium sulfate, given 

 together with sugar, would increase the number of roots of IB-treated 

 defoliated cuttings so much that it was equal to that of IB-treated leafy 

 cuttings. This is represented by point F in Figure 6. The same treatment 

 given to leafy cuttings did not further increase the number of roots 

 formed (curve FD). 



Since it is unlikely that leaves would contribute ammonium sulfate 

 to the cutting, a search was made for more likely substances. Among the 

 most promising of these is arginine. When tested in the presence of 4 

 per cent sucrose 10 ppm. of arginine would produce an effect equivalent 

 to 1,000 ppm. of ammonium sulfate (52). Since both arginine and sucrose 

 are natural constituents of the plant it seems reasonable to assume that 

 one of the functions of the leaf is to provide cuttings with these com- 

 pounds, which then together with auxin cause root formation. 



Arginine has recently also been recognized as a co-factor for auxin 

 action in the elongation of the Avena coleoptile (4); it has a function as 

 a high energy phosphate acceptor and accumulator. This would make 

 its action as a cofactor to auxin understandable because auxin itself 

 appears to be intimately connected with the phosphate metabolism of 

 the plant, possibly with the transfer of high energy phosphate. 



Weeding 



With respect to dollar volume of sales, 2,4-D for weed control un- 

 doubtedly constitutes the most important use of a synthetic plant hor- 

 mone. In 1948 an estimated 16,000,000 pounds of 2,4-D compounds 

 were manufactured and sold at an average price of $0.75 per pound 

 (21). This compound is most frequently used as a selective herbicide on 

 crops belonging to the family of the Gramineae. Consequently, it is 

 finding its major use in the tropics in the culture of sugar cane (55). 

 The aerial portions of sugar cane are practically completely resistant 

 to 2,4-D sprays (49), but its roots are quite sensitive (7). 



Against susceptible tropical sugar cane weeds such as Commelina and 

 Ipomea, 2,4-D is highly eflfective. The small dosages necessary to kill 

 these weeds make low-volume applications of 2 to 4 gallons per acre 

 feasible. When the acreage involved is large enough such low-volume 

 sprays can be best applied by plane. Most efficient of these sprays is 

 2,4-D in an ester form dissolved in oil, which, however, can be flown on 

 safely only at times when there is a minimum danger of drift, and, as an 



