ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 59 



Do Healtliy Plants Exhale Ammonia ?— The idea having 

 been advanced that in tlie act of vegetation a loss of ni- 

 trogen may occur, possibly in the form of ammonia, Knop 

 made an cxjieriment with a water-plant, the Typha latl- 

 folia., a species of Cnt-tail, to determine this point. The 

 plant, growing imdisturbed in a pond, was enclosed in a 

 glass tube one and a half inches in diameter, and six feet 

 long. The tube was tied to a stake driven for the purpose ; 

 its lower end reached a short distance below the surface 

 of the water, while the uppiT end was covered air-tight 

 with a cap of India rubber. This cap was penetrated by 

 a narrow glass tube, which communicated with a vessel 

 filled with splinters of glass, moistened with pure hydro- 

 chloric acid. As tlie large tube was placed over the plant, 

 a narrow U-shaped tube was immersed in the water to 

 half its length, so that one of its arms came within, 

 and the other without, the former. To the outer extremity 

 of the U-tube was attached an apparatus, for the perfect 

 absorption of ammonia. By aspirating at the upper end 

 of the long tube, a current of ammonia-free air was thus 

 made to enter the bottom of the apparatus, stream upward 

 along the plant, and pass through the tube of glass-splint- 

 ers wet with hydrochloric acid. Were any ammonia 

 evolved within the long tube, it would be collected by the 

 acid last named. To guard against any amuionia that 

 possibly might arise from decaying matters in the water, 

 a thin stratum of oil was made to float on the water with- 

 in the tube. Through this arrangement a slow stream of 

 air was passed for fifty hours. At the expiration of that 

 time the hydrochloric acid was examined for ammonia ; 

 but none was discovered. Our tests for ammonia are so 

 delicate, that we may Avell assume that this gas is not ex- 

 haled by the Typha lati folia. 



The statements to be foi;nd in early authors (Sprengel, 

 Schiibler, Johnston), to the effect tliat ammonia is exhaled 

 by some plants, deserve further examination. 



