GROWTH SUBSTANCES-RED LIGHT INTERACTIONS 183 



tinuous exposure to red light failed to give a greater effect.- Far-red 

 radiation was obtained from five 200-watt incandescent bulbs at a 

 distance of about 60 cm. and separated from the tissue by four layers 

 each of red and blue cellophane and 7 cm of water. Twenty minutes 

 was used as a standard exposure, since it gave a maximal effect, with 

 10 min significantly less effective. 



Indoleacetic acid was obtained from Eastman Chemical Company, 

 gibberellic acid from Merck and Company, and kinetin from Nutri- 

 tional Biochemical Company. 



RESULTS 



All data presented and discussed have been confirmed in at least 

 three repetitions. While absolute values varied considerably between 

 experiments, the relationships observed were consistent throughout. 



Effects of Red and Far-Red Treatments on Endogenous Growth 



When excised sections are placed in basal medium, some elongation 

 takes place without added growth substances. This will be referred to 

 as "endogenous growth." Figure 1 shows the effects of red and far-red 



4 



2 3- 

 o 



H 



<2- 

 e> 



z 

 o 



_J 



UJ 



Dg 



FR 



J1 



R 

 FR 



Rg 



M 



PR 



R 



Fig. L Elongation of sections from dark-grown (Dg) or red-grown 

 (Rg) plants. Sections initially 8 mm long, cut 4 mm from apex. Treat- 

 ments at start of 20-hr growth period in darkness: C, dark controls; R, red 

 light (100 min. 1950 kiloergs/cm-) ; FR, far red (20 min); R FR, red 

 followed by far red; etc. Divisions of bars represent replicate means of 

 10 sections. (Dg exp. 4-4-57; Rg exp. 2-22-57.) 



- Since the presentation of these results, A. W. Galston has found that 30 sec 

 exposure (about 10 kiloergs/cm-) has a maximal effect when the most apical 

 section is used. 



