380 APPENDIX E. 



II. — Experiments of Stohmann. 



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 been 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 dis- 

 tilled 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 reaction. The solution must 

 always react, slightly acid, and be maintained 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. \Miilst 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 ex- 

 periments, 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 



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

 acid continuously from tlieir roots. 



