676 LIGHT AND LIFE 



A. Experiments with L. perpusilla 6746 



1. Interaction of low temperature and chelating agents. Attempts to 

 repeat some of the results mentioned above under slightly different 

 conditions met with difficulty in obtaining complete inhibition of 

 flowering by chelating agents under long-day conditions. Tests of 

 white fluorescent light intensities ranging from 10 to 800 footcandles 

 suggested that this was not a factor of importance. Since the effect 

 of chelating agents on photoperiodic requirements could in a sense 

 be mimicked by high temperatures, it seemed possible that low tem- 

 peratures might partially reverse it. Several experiments confirmed 

 this possibility, indicating, for example, that levels of EDTA or 

 citrate which would completely inhibit flowering under 16 hours 

 of light at 27 °C would permit some flowering at 21.5°C. This effect, 

 however, is small, and seemed unlikely to account completely for the 

 difficulties experienced. The pH factor was the next considered, and 

 proved to be crucial. 



2. pH and the action of chelating agents. Loav pH levels, about 

 4.0, had been used in the experiments in which difficulties arose. The 

 original reason for this was the observation (8) that cultures plus 

 or minus EDTA differed in vegetative growth mainly at higher pH 

 levels, so that the use of low p¥L provided more comparable controls. 

 However, closer attention to the known properties of chelating agents 



(2) suggested, and subsequent experiments showed, that the action 

 of either EDTA or citrate in this system is extremely dependent on 

 pH, being greatly reduced at low values. 



Results of a typical experiment are presented in Fig. 1. Cultures 

 in 125-ml erlenmeyer flasks containing 50 ml of medium were grown 

 at 26°C under 120 footcandles of continuous cool white fluorescent 

 light. The basic medium was M with 1 % sucrose adjusted to an 

 initial pH of either 3.6 or 4.6, and each pH level contained 0. 

 3. .8 X 10"'' ^' oi" 10— "5 M EDTA. On the third day of the experi- 

 ment, all the fronds in each culture were transferred to similar flasks 

 of fresh medium; the pH changed less than 0.2 unit in these first 

 three days. Growth was healthy in all cultures but somewhat slower 

 at the low pH. All cultures (containing 40-60 fronds each) were dis- 

 sected on the sixth day, giving the FL% values shown. EDTA was 

 much more effective at pH 4.6 than at pH 3.6, although the pH 

 made no difference in the control media. Almost superimposable 

 results were obtained in a similar experiment with citrate at con- 

 centrations 100 times as high, and the general pattern is easily re- 

 peatable. The wide scatter in the points for EDTA at low pH al- 



