EFFECT OF BORON ON THE GROWTH OF CERTAIN GREEN PLANTS

Abstract

1. Under the usual water-culture methods boron proved toxic to Spirodela polyrhyza at concentrations of above 1 p.p.m. Toxicity was evident in reduced growth, smaller plants, and loss of roots. In concentrations above 5 p.p.m. death soon occurred. Chlorosis was noted in all the cultures but those plants with boron were slightly more chlorotic than the controls. In both cases the addition of inorganic iron was without effect, but the addition of potassium tartrate at a concentration of 20 p.p.m. resulted in a marked chlorophyll development in all the cultures. 2. Under pure culture conditions boron seemed to increase growth at certain concentrations. At a concentration of 5 p.p.m. toxicity was apparent. No chlorosis was noted with boron. 3. With Chlorella under pure culture conditions marked stimulation was noted in experiments 6 and 7 with concentrations up to 10 p.p.m. and even with higher concentrations In experiments 8, 9 and 10 no stimulation was noted. 4. Chlorella proved extremely resistant to boron. A concentration of 30 p.p.m. was required to decrease growth on experiment 6 while in experiment 9 toxicity was noted at a concentration of 10 p.p.m. as evidenced by decreased growth, but survived at a concentration of 140 p.p.m. No chlorosis was noted in any case. 5. The addition of sodium citrate or potassium tartrate, both of which tend to increase iron availability did not decrease the toxicity of boron when growth was taken as the criterion. 6. The addition of dextrose to the culture medium increased growth as expected and made Chlorella much more resistant to boron. This was likewise true of sucrose. 7. Boron did not decrease the availability of iron. 8. Boron was not found present in the precipitation formed in the culture medium. The method of analysis used was not very sensitive.