270 Journal of Agricultural Research voi. xviii, no. s 



The stimulating action of calcium carbonate was observed with all the 

 different kinds of seedlings studied. Its effect on lemon and grapefruit 

 seedlings is illustrated in Plate 33, C-F. 



Carbon dioxid was passed through carbon-treated water containing 

 an excess of calcium carbonate. The resulting solution was found upon 

 analysis to contain over 400 parts per million calcium as calcium 

 bicarbonate. After portions were withdrawn and slightly agitated to 

 expel the excess of carbon dioxid, citrus seedlings were introduced 

 into the solution. With all the seedlings tried a stimulating effect was 

 noticeable. 



AMELIORATING ACTION OF LIME AND ORGANIC MATTER WHEN 

 ADDED TO TOXIC SOLUTIONS 



A slightly toxic solution was prepared by mixing one part of untreated 

 distilled water with three parts carbon-treated water. This gave a solu- 

 tion that would stop the root development of all the seedlings. The 

 addition of calcium carbonate (solid phase present) and organic matter 

 to this solution invariably enabled the plant to overcome the toxic effect 

 of the solution. Many tests of this kind were made with all kinds of 

 citrus seedlings. A fair example of the relative root development of a 

 i2-day-old culture of grapefruit seedlings is shown in Table III. 



Table III. — Protective action of litne and organic extracts 



Treatment. 



Toxic water, control 



Toxic water, plus 20 p. p. m. organic matter 



Toxic water, plus calcium carbonate (solid phase present) , 



Root devel- 

 opment. 



Mm. 



O 



148 



Calcium is known to have a marked antagonism to the toxicity of some 

 inorganic salts. The protective and stimulating action of the calcium 

 carbonate is, however, in this instance not explainable on this basis. 

 Citrus seedlings showed no growth in toxic water mixtures to which 10 

 parts per million of calcium sulphate or of calcium chlorid had been 

 added. The solubility of calcium carbonate in distilled water is approx- 

 imately 10 parts per million. From the fact that calcium chlorid and 

 calcium sulphate in the same concentration showed no protective action 

 it appears that it is not the calcium ion itself that gives rise to the antago- 

 nistic action on distilled water toxins. Furthermore, the calcium content 

 of the organic dried peat extract was only 0.3 per cent, so that protective 

 action of the peat in concentrations of 20 parts per million is not 

 attributable to the calcium it contains. Though the nature of the pro- 

 tective action has not been determined, the adsorption of the toxins on 

 the calcium carbonate particles present in the solid phase and by the 

 colloidal organic constituents is suggested as a possible explanation. 



