AtMOSPHEIllC AIU AS TIIK FOOD OF PLANTS. 57 



air-tight, upon a glas^s plate, and having two glass tubes 

 cemented into its neck above, as in fig. 6. Tlirough 

 an aperture in the centre of the glass ])late the stem of 

 the plant experinienled on was introduced, so that its fo- 

 liage should occupy the bell, while the roots were situated 

 in a pot of earth beneath. Two young bean-plants, grow- 

 ing in river sand, were arranged, each in a separate appa- 

 ratus, as in the figure, on June 19th, 1859, their stems be- 

 ing cemented tightly into the opening below, and through 

 the tubes tlie foliage of each plant received daily the same 

 quantities of mois^t atmosj)heric air mixed with 4-5 per 

 cent of carbonic acid. One plant was supplied in addition 

 with a quantity of carbonate of ammonia, w^hich Avas in- 

 troduced by causing the air that was forced into the bell 

 to stream through a dilute solution of this salt. Both 

 plants grew well, until the experiment was terminated, on 

 the 11th of August, when it Avas found that the plant 

 Avhose foliage was not supplied with carbonate of ammo- 

 nia weighed, dry, 4.14 gm., while the other, which Avas 

 supplied Avith the A\apor of this salt, weighed, dry, 6.74 

 gms. Tlie fir>t plant had 20 full-sized leaves and 2 side 

 slioots; the second Ixid 40 leaves and 7 shoots, besides a 

 much larger mass of roots. The first contained 0.106 

 gm. of nitrogen; the second, double that amount, 0.208 

 gm. Other trials on various [»lants failed from the diffi- 

 culty of making them groAV in the needful circumstances. 



Th#absorption of ammonia by foliage does not appear, 

 like that of carbonic acid, to depend upon the action of 

 sunlight ; but, as Mulder has remarked,* may go on at 

 all times, especially since the juices of plants are very fre- 

 quently more or less charged with acids which directly 

 unite chemically with ammonia. 



When absorbed, ammonia is chiefly applied by agricul* 



• Cheraie der Ackerkriime, A'ol. 2, p. 211. 



3* 



