220 GROWTH OF PLANTS 



has been found that spraying only open flowers causes approximately 100 per 

 cent set. 



Another method of applying growth substances is to remove the style 

 with small scissors and apply a lanolin preparation directly to the cut 

 surface. For this purpose 0.1 to 0.3 per cent of ^-indolebutyric acid in 

 lanolin has been recommended. Less of other chemicals is required, as fol- 

 lows: i3-naphthoxyacetic and propionic acids 0.05 per cent, Q!-(2-chloro- 

 phenoxy)-propionic acid 0.01 per cent. 2,4-Dichlorophenoxyacetic acid is 

 not recommended for this method since it causes modification of leaves 

 even when used in very low concentrations. 



The vapor method of treating flowers throughout the entire house is 

 effective, but mhibition of growth of the entire plant after the treatment 

 may result. If used, the ethyl or methyl esters of /3-naphthoxyacetic acid 

 or Q:-(2-chlorophenoxy)-propionic acid are recommended. Twenty-five to 

 50 mg per 1000 cubic feet of space vaporized by means of a warm electric 

 plate are recommended. The heat should be applied so that the vapor 

 rises slowly in the course of an hour. The air should be agitated by means 

 of an electric fan. 



The aerosol method of applying growth substances has recently been 

 emphasized. It is a kind of modification of a fine spray. One of the best 

 methods of applying aerosol is to place the gro^\^h substance with sesame 

 oil in the cylinder with Freon (dichlorodifluoromethane) . The internal 

 pressure resulting is approximately 150 pounds. The mixture, dispensed 

 through a small aperture, makes a mist or fog which affects the entire 

 plant. When used in a greenhou^^e of 2000 cu. ft. capacity with tomato 

 plants having open flowers, 50 to 450 mg of ethyl a-(2-chlorophenoxy)- 

 propionate were found sufficient to set fruit on all the plants. The aerosol 

 method is subject to the same objection as the vapor method. 



2,5-Dichlorobenzoic acid applied to the soil of potted tomato plants 

 mduced seedless fruit. One to 5 mg in 50 cc of water applied to the soil of 

 a 4-inch pot were sufficient to induce fruit set of open flowers and also 

 flowers growing on the plant for one month thereafter. This method has 

 more theoretical than practical value at the present time. 



The formative influence of growth substances. A new line of plant 

 hormone research was started when it became known that some substances 

 had a formative influence on growth, modifying organs in size, shape, 

 pattern, and texture. ^o- 43. 44. 45, 46, 57. 58. 59 Formative effects were evident 

 on new growth which occurred within days or weeks after the plant was 

 treated. This was in contrast to induced curvatures due to cell elongation 

 which took place within a few minutes after treatment. Fig. 82 illustrates 

 a type of formative influence which 4-chlorophenoxyacetic acid has on the 

 growth of tobacco plants. 



Three groups of chemicals, (3-naphthoxy, substituted chlorophenoxy, and 

 substituted benzoic acids, were outstanding for their formative mfluence, 



