356 APPENDIX E. 



II. Experiments of StoJimann. 



The experiments of Stohmann agree in their main results with 

 those of Knop. According to these experiments, the maize plant 

 grows to full maturity if in the beginning of May the seed which 

 has germinated in water, and has shot forth roots, is placed in a 

 solution containing the food of maize in the proportions in which 

 they exist in the ashes, if at the same time there has heen added 

 to it so much nitrate of ammonia that to every part of phosphoric 

 acid in the solution there are two parts of nitrogen, and if finally 

 it has been diluted with distilled water to a concentration of three 

 parts of solid matter per 1000 parts. The plants must grow in 

 a sunny spot, and the water exhaled by the leaves must be daily 

 replaced by distilled water, and the solution tested as to its reac- 

 tion. The solution must always react, slightly acid, and be main- 

 tained in this condition by the addition from time to time of a few 

 drops of phosphoric acid. If these conditions are fulfilled, there is 

 no necessity for any artificial source of carbonic acid, but by means 

 of the atmospheric carbonic acid alone there are produced fully 

 formed plants which, under favourable circumstances, attain a 

 height of 7 feet.* 



The experiments of Stohmann were more especially directed to 

 the influence exercised on the growth of the maize plant by the 

 withdrawal of one element of food. In this point the results differ 

 from those of Knop. Whilst in the experiments of the latter, 

 maize was found to grow perfectly without silicic acid, soda, or 

 ammonia, Stohmann made use of silicic acid in all his experiments, 

 and found further that by the complete withdrawal of ammonia 

 and even soda the plants grew quite well. 



On withdrawing ammonia completely and replacing it by nitric 

 acid, Stohmann found that the plants grew perfectly well for the 

 first ten to twelve days, then they became of a pale yellowish 

 green, and the vegetation proceeded extremely slowly. 



If after a month's vegetation a little ammonia (in the form of 

 nitrate or acetate) was given to the plants, they died very quickly. 

 Without this supply of ammonia the blanched, sickly vegetation 

 continued ; the plant did not die, and yet it could not be said to 

 live.t In the experiments made without soda, it was found that 

 the plant could dispense with this substance at first, but its pro- 

 gress was soon arrested if the soda was completely withdrawn. 

 The nitrate of lime of the normal solution was in another experi- 

 ment replaced by a corresponding quantity of nitrate of magnesia. 

 The growth of the maize plant was after a short time much re- 

 tarded, only a few small, thin leaves being developed. By the ad- 

 dition of a little nitrate of lime to the growing plant, the most 



* According to Knop maize plants growing in a watery solution give off 

 carbonic acid continuously from their roots. 



t Compare Knop, ' Chem. Central Bl. 1862,' s. 257. 



