ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 49 
plants in which the microscope reveals chlorophyll, although 
the prevailing color may be other than green. 
Influence of Light on Fixation of Carbon.—As men- 
tioned, Ingenhouss (in 1779) discovered that oxygen gas 
is given off from foliage, and carbon fixed in the plant 
only under the influence of light. Experiments show that 
when a seed germinates in exclusion of light it not only 
does not gain, but steadily loses weight from the consump- 
tion of carbon (and hydrogen) in slow oxidation (respira- 
tion). 
Thus Boussingault (Comptes .Rendus, 1864, p. 883) 
caused two beans to germinate and vegetate, one in the 
ordinary light and one in darkness, during 26 days. The 
gain in light and loss in darkness in entire (dry) weight, 
and of carbon, etc., are seen from the statement below. 
In Light. In Darkness. 
Weight of seed...... 0 922 gram... ccc cee cee 0.926 gram. 
Weight of plant..... 15208: SE os Seat eence cua’ 0.566 
Gain = 0.871 gram. Loss... .0.360 gram. 
Carbon, Gain = 0.1926 * Loss...0.1598  ‘* 
Hydrogen, “* = 0.0200 “ “ .,.0,0282 
Oxygen, “ = 01591 “ “ ,..0.1766 
§ 6. 
THE AMMONIA OF THE ATMOSPHERE AND ITS RELATIONS 
TO VEGETABLE NUTRITION. 
Ammonia is a gas, colorless and invisible, but having a 
peculiar pungency of odor and an acrid taste. 
Preparation.—It may be obtained in a state of purity by heat- 
ing a mixture of chloride of ammonium (sal ammoniac) and quicklime. 
Equal quantities of the two substances just named (50 grams of each) 
are separately pulverized, introduced into a flask, and well mixed by 
shaking. A straight tube 8 inches long is now secured in the neck of 
the flask by means of'a perforated cork, and heat applied. The ammonia 
gas which soon escapes in abundance is collected in dry bottles, which 
are inverted over the tube. The gas, rapidly entering the bottle, ina 
few moments displaces the twice heavier atmospheric air. As soon as a 
3 
