p. W. ZIMMERMAN 85 



recognized for complete fertilizers. The scant claims for such stimulation 

 have not stood the test of time. 



Flowers of solanaceous plants last for an abnormally long time after 

 being treated with hormone-like substances which induce parthenocarpic 

 development. This fact is very suggestive and gives the idea that the 

 Hfe of cut flowers can be prolonged. To date, unfortunately, these 

 phenomena seem to apply only to intact plants. No effective means for 

 substantially increasing the life of cut flowers have been discovered. 

 Attempts, however, to find methods or chemicals for this purpose should 

 not be discouraged. 



From our experience with substances which induce roots, modify 

 leaves, and otherwise regulate growth, it appears evident that aU organs 

 of the plant are under some regulating influences probably of a chemical 

 nature. It would seem, therefore, that we should find flower-inducing 

 substances and shoot-inducing substances. While there have been various 

 claims for shoot-inducing substances, this is not a reality in the same sense 

 that we have root-inducing substances. There is a special case reported 

 where leaves of the pineapple plant produce many adventitious buds 

 after treatment with 2,4-D. Other species have not responded in like 

 manner. It is logical, however, to assume that such chemicals do exist in 

 nature and eventually may be found. Once located, if they ever should 

 be, progress should be rapid and results spectacular. 



One of the greatest single problems in agriculture and horticulture 

 is the control of weeds. For many years one of the farmer's greatest 

 problems has been cultivation largely to rid the field of weeds. However, 

 that situation is changing rapidly since the discovery that hormones can 

 be used to regulate and actually kill troublesome weeds. Lawns can be 

 sprayed to rid them of such weeds as dandelion, plantain, and hawkweed 

 without kilhng the grass. Interestingly enough, 2,4-D can be applied 

 along with fertilizer to kill the weeds while the grass is being stimulated. 



Weed killing is by far the most important practical use of hormone-hke 

 chemicals. The second in importance is the use of naphthaleneacetic 

 acid to prevent preharvest drop of apples. 2,4-D alone has a potential 

 annual market of more than 100,000,000 pounds and may soon top the 

 list of all organic agricultural chemicals. 



There are also other achievements with plant hormones, and these 

 illustrate the varied lines of attack from the practical point of view. 

 In Hawaii several kinds of plant hormones are being used to force 



