August 4, 1905.] 



SCIENCE. 



147 



original solution. Table II. presents the data 

 for this experiment as well as for the two 

 following ones. Relative transpirations on 

 the basis of 100 for the original nutrient solu- 

 tion of 15 parts per million are given. There 

 was a marked increase in the growth of the 

 plants, with the addition of each one of the 

 salts, but none of thera produced as good 

 plants as did the combination of all four salts. 

 In experiment VIII. the same solution of 

 15 parts per million was increased in concen- 

 tration by the addition of 60, 140, Y35 and 

 1,535 parts per million of calcium sulphate. 

 Thirty-six seedlings were grown in each solu- 

 tion for thirteen days, comparison being again 

 made with the original solution. The increase 

 in transpiration was also very marked in this 

 case, as is shown by the data in Table II. 

 Here the transpiration figures tend to show a 

 depressing effect in the solution of highest 

 concentration, as in the former case. This 

 experiment was repeated with similar results. 



Table II. 

 Data for Experiments VII. to IX. 



Experiment 

 VII., 24 

 plants, 13 



Experiment 

 VIIL, 36 

 plants, 13 

 days. 



Experiment 

 IX., 60 

 plants, 15 

 days. 



Nutrient solution, 15 p. p.m. 

 Do. + 140 p. p. m. CaSb^. 

 Do. -f 140 p. p. m. MgHPO^. 

 Do. + 140 p. p. m. KXO^- 

 Do. + 140 p. p. m. NaNOj. 

 Do. + 140 p. p. m. of four 



above salts, inchem.equiv. 



amounts. 

 Nutrient solution, 15 p. p. m. 

 Do. + 60 p. p. m. CaSO^. 

 Do. 4-140p. p. m. CaSO^. 

 Do. + 735 p. p. m. CaSO^. 

 Do. + 1535 p. p. m CaSO^. 

 Nutrient solution, 15 p. p.m. 

 Do. + 60 p. p. m. NaCl. 

 Do. + 140 p. p. m. NaCl. 

 Do. -I- 735 p. p. m. NaCl. 

 Do. + 1535 p. p. m. NaCl. 



100.0 

 205.5 

 143.5 

 224.4 

 156.2 

 241.9 



100.0 

 117.8 

 157.7 

 188 9 

 155.5 

 100.0 

 111.1 

 114.9 

 117.2 

 95.4 



Sodium chloride, which furnishes none of 

 the elements usually classified as ijlant food 

 materials, was also used to increase the con- 

 centration of the original solution. Sixty 

 plants were used in this case, being grown for 

 fifteen days. The treatment was the same as 



that with calcium sulphate just described, and 

 the results showed the same general effect, 

 although the actual differences between the 

 different cultures were not nearly as great. 

 The last fact is probably due to the toxic 

 effect of the chlorine ion, tending to retard 

 growth and thus partially masking the effect 

 of concentration. The data are given in 

 Table 11. 



From the experiments thus far described it 

 is evident that there is an optimum physical 

 concentration of the nutrient solution at 

 which water cultures of wheat thrive best, 

 aside from variations in the amounts present 

 of the different nutrient materials. In the 

 solutions of lower concentration the retarding 

 factor for plant growth is not necessarily con- 

 nected with the low osmotic pressure, for the 

 same acceleration of growth which is observed 

 to accompany an increase in concentration 

 can be obtained by entirely different means. 

 The author has already called attention to the 

 fact that both nutrient solutions and soil ex- 

 tracts are greatly improved for the growth of 

 wheat by addition of small quantities of the 

 practically insoluble bodies, carbon black and 

 ferric hydrate^ and that the beneficial effect 

 of these bodies is due to their power to absorb 

 toxic substances. Such toxic materials are 

 present in many soils, and physiologically 

 similar ones are given off by the ^ roots of 

 wheat grown in water culture.* The addition 

 of these insoluble bodies to a weak nutrient 

 solution can not possibly increase its concen- 

 tration to any appreciable degree; indeed, 

 such addition is apt to decrease its concentra- 

 tion to some extent owing to phenomena of 

 adsorption. Yet such treatments result in the 

 same sort of acceleration of growth as is ob- 

 tained with increase in concentration. 



Dr. B. E. Livingston, of the bureau of soils, 

 has made possible a quantitative comparison 

 in this regard by furnishing the author with 



■ - Breazeale, J. F., ' Effect of Certain Solids upon 

 the Growth of Wheat in Water Cultures,' about 

 to appear in the Botanical Gazette. 



^ In this regard see Livingston, B. E., Britton, 

 J. C, and Reid, F. R., ' Studies on the Properties 

 of a Sterile Soil, U. S. Dept. Agric., Bureau of 

 Soils, Bui. No. 28. 



