THE MOLECULAR FORCES IN PLANTS. 243 



the membranes of the root-cells act upon the stones and other 

 elements of the soil ; corrosive action is set up, and the sub- 

 stances dissolved are absorbed by the plant. 



From the following experiments which I recently made, but 

 which need to be carried still further in order to definitely 

 establish the relations in question, it appears to me to follow that 

 not only Carbon dioxide and organic acids, but also Hydrochloric 

 acid, are to be .regarded as substances which are of importance in 

 setting up corrosive action. We grow maize plants by the water- 

 culture method (see 1) in a fluid which contains in 1000 gr. of 

 water, 1'OOgr. of Calcium sulphate, 0'25 gr. of Potassium chloride, 

 0'25 gr. of Magnesium sulphate, 0'25 gr. of acid Potassium 

 phosphate, and a little Ferric chloride. The culture vessels need 

 be large ; it is sufficient if they contain 250 c.c. of fluid. When the 

 maize plants have developed their fourth leaf in the non-nitrogen- 

 ous food solution, they are at any rate in a high state of Nitrogen 

 starvation. Two maize plants are now removed from the food 

 solution, and transferred to two vessels, of which one contains 

 water, a, the other a O'l per cent, solution of Ammonium chloride, 

 b. A third vessel, c, is provided with Ammonium chloride solution 

 alone, without a plant; one plant is left in the non-nitrogenous 

 food solution, d ; another likewise remains in the original food 

 solution, after Ammonium chloride solution (O'l gr. in 100 c.c. of 

 water) has been added to it, e. After about eight days strips of 

 blue litmus paper are dipped for thirty seconds into the fluids in 

 b and e, others for fifteen seconds into the fluids in a and d, and 

 then for fifteen seconds into the fluid in c. The strips of litmus 

 paper introduced into b and e become more intensely red in colour 

 than the other two, which can only be explained on the assump- 

 tion that the Ammonium chloride has been decomposed by the 

 plants with formation of free Hydrochloric acid. The Ammonium 

 chloride penetrating into the tissues of the plants meets with 

 organic acids in the cells. These decompose the chloride, and 

 since the Hydrochloric acid thus formed is not made use of by the 

 plants, it escapes into the food solution, and increases its acidity. 



To convince ourselves that organic acids, even outside the plant, 

 can decompose chlorides with formation of Hydrochloric acid, the 

 following experiments may be made : 



We obtain two beakers and pour into each 500 c.c. of distilled 

 water. To a we add 3 gr. of Oxalic acid; to &, 3 gr. of Oxalic 

 acid and 0'4 gr. of Sodium chloride. We now suspend in each 



