ir 
< = 
\ 
> 
o 
ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 59 
Do Healthy Plants Exhale Ammonia ?—The idea having 
been advanced that in the act of vegetation a loss of  ni- 
trogen may occur, possibly in the form of ammonia, Knop 
made an experiment with a water-plant, the Zypha lati- 
folia, a species of Cat-tail, to determine this point. The 
plant, growing undisturbed 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 upper 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 the large tube was placed over the plant, 
anarrow 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 Jast named. To guard against any ammonia 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 well assume that this gas is not ex- 
haled by the Typha latifolia, 
The statements to be found in early authors (Sprengel, 
Schiibler, Johnston), to the effect that ammonia is exhaled 
by some plants, deserve further examination. 
