Transpiration of wheat seedlings as affected by soils, by solutions of different densities, and by various chemical compounds

In the foregoing investigation an attempt was made to study the effect of different densities of solutions and of various chemical compounds upon the relative transpiration of plants. The results obtained may be summarized as follows: The transpiration per gram of dry matter of wheat seedlings grown in solution, sand, and soil cultures containing 4,500, 2,250, 750, 375, 187.5, 93.5 and 0.0 p.p.m. respectively of a complete nutrient solution, increased in every case with the decrease in density down to a certain point and then decreased with the further diminution in concentration; while the actual dry matter produced increased with the rise in density. This general run of the relative transpiration was explained thus: The increase from the highest concentration to that where the change occurs, was thought might be due to the decreased osmotic pressure of the solution and to the decreased density of the cell sap; while the decrease from where the change occurs to the lowest density, was believed might be due to the decreased stimulative action of the dilute solutions. The relation of the density of the solution to that of the cell sap was tested experimentally and it was found that the density of the latter increased with the concentration of the former. The relative transpiration of corn and bean seedlings grown in solution, and in sand cultures containing the same solutions as above, also tended to increase with the reduction in density down to a certain dilution and then diminish with the further decline in concentration; while the plant growth tended to increase with the concentration. Both the corn and bean seedlings transpired less water per gram of dry matter than the wheat seedlings, and the beans less than the corn. The correlative transpiration of wheat seedlings grown in solution and in sand cultures treated with the same number and strength of densities as above, of NaCl and Na2SO4, with each density containing exactly the same amount of a complete nutrient solution, increased in the solution cultures of both non-nutrient salts from the highest density to that of the lowest; in the sand cultures of the same salt solutions it tended to increase with the decrease in density down to a certain point and then to diminish with the further reduction in concentration. The plant growth in this case was greatest in the intermediate densities. The relative transpiration of wheat seedlings grown in different densities of agar containing the same amount of a nutrient solution increased with the decrease in density. By increasing the amount of Ca(NO3)2, KCl and Na2HPO4 in a complete nutrient solution, the relative transpiration of the wheat seedlings grown in solution cultures and sand cultures containing these solutions, decreased in the case of the Ca(NO3)2 with the increase in density; but increased in the case of the Na2HPO4, while in the case of the KCl it diminished in the sand cultures but increased in the solution cultures. Fiftieth normal solutions of NaNO3, KNO3, Na2HPO4, K2HPO4, Ca(NO3)2, CaCl2, KCO3, (NH4)2CO3, (NH4)2SO4, MgSO4, and MgCl2, to each one of which was added exactly the same amount of a complete nutrient solution, affected the relative transpiration of the wheat seedlings grown in solution and sand cultures very differently, and the order of magnitude of this effect was not exactly the same in both kinds of cultures for all the salts. In the solution culture the relative transpiration was inhibited in this order: (NH4)2CO3 greater than MgSO4 greater than MgCl2 greater than K2CO3 greater than (NH4)2SO4 greater than KNO3 greater than Ca(NO3)2 greater than NaNO3 greater than CaCl2 greater than Na2HPO4 greater than K2HPO4; while in the sand culture it was reduced thus: (NH4)2SO4 greater than (NH4)2CO3 greater than MgSO4 greater than Ca(NO3)2 greater than MgCl2 greater than KNO3 greater than CaCl2 greater than K2CO3 greater than NaNO3 greater than Na2HPO4 greater than K2HPO4. In both cases the non-nutrient