56 HOW CROPS FEED 
by plants as food is most abundantly established. The 
salts of ammonia applied as manures in actual farm prac- 
tice have produced the most striking effects in thousands 
of instances. 
By watering potted plants with very dilute solutions of 
ammonia, their luxuriance is made to surpass by far that 
of similar plants, which grow in precisely the same condi- 
tions, save that they are supplied with simple water. 
Ville has stated, 1851-2, that vegetation in conserva- 
tories may be remarkably promoted by impregnating the 
air with gaseous carbonate of ammonia. For this purpose 
lumps of the solid salt are so disposed on the heating ap- 
paratus of the green-house as to gradually vaporize, or 
vessels containing a mixture of quicklime and sal ammo- 
niac may be employed. Care must be taken that the air does 
not contain at any time more than four ten-thousandths 
of its weight of the salt; otherwise the foliage of tender 
plants is injured. Like results were obtained by Petzholdt 
and Chlebodarow in 1852-3. 
; Absorption of Ammonia by Foli- 
age.—Although such facts indicate 
that ammonia is directly absorbed by 
foliage, they fail to prove that the 
soul is not the medium through which 
the absorption really takes place. We 
remember that according to Unger 
and Duchartre water enters the 
higher plants almost exclusively by 
the roots, after it has been absorbed 
by the soil, To Peters and Sachs 
(Chem. Ackersmann, 6, 158) we owe 
an experiment which appears to de- 
monstrate that ammonia, like carbonic 
acid, is imbibed by the leaves of 
Fig. 6. plants. The figure represents the ap- 
paratus employed. It consisted of a glass bell, resting below, 
