MANURING PLANTS THROUGH THEIR LEAVES. 549 



which is capable of entering into combination with carbonic 

 acid, and of forming a volatile salt. Ammonia in its gaseous 

 form, as weU as all its volatile compounds, is of extreme 

 solubility in water. Ammonia, therefore, cannot remain long 

 in the atmosphere, as every shower of rain must effect its 

 condensation, and convey it to the surface of the earth. Hence, 

 also, rain-water must at all times contain ammonia, though not 

 always in equal quantity. It must contain more in summer 

 than in spring or in winter, because the intervals of time 

 between the showers are in summer greater ; and when several 

 wet days occur, the rain of the first must contain more of it 

 than that of the second. The rain of a thunderstorm, after a 

 long-protracted drought, ought, for this reason, to contain the 

 greatest quantity conveyed to the earth at one time." 



TMs fact has been occasionally applied to the improvement of the air 

 of glass-houses, by mamiritig plants through their leaves. When the 

 philosopher of Giessen demonstrated the important truth that ammonia 

 is derived from the atmosphere, a new light was thrown upon the 

 refreshing and invigorating effect of heavy rains, which act, not 

 merely by their water, as once was thought, but also by the car- 

 bonate of ammonia which they bring down. So far as agriculture is 

 concerned this is, however, a truth devoid of possible application, 

 because the volatile carbonate cannot be advantageously used, arti- 

 ficially, through the agency of the atmosphere. But it is otherwise 

 with gardeners, who have to create an artificial atmosphere in a con- 

 fined space. It is not a little remarkable, then, that so simple an 

 agent, so easily procured, and applicable with so little trouble, should 

 have scarcely ever been employed in hot-houses in the proper manner. 

 Where it has been used it has been almost invariably when dissolved 

 in water, and applied with a syringe. 



The carbonate of ammonia of the atmosphere is suspended, dissolved 

 in invisible vapour. In this state it is incessantly in contact with 

 every part of the foliage. When rain falls, the ammonia disappears 

 for the moment, passing downwards in the rain-drops to the ground, 

 and thence arriving at the roots of plants. But if it is in gardens first 

 dissolved in water, and then thrown upon plants with a syringe, natural 

 conditions are by no means imitated. It reaches no part except that 

 on which the water falls, half the upper surface and nearly all the under 

 surface of the foliage is missed, and it is scarcely detained even upon 

 the parts which the water actually touches. The proper course is to 

 throw it into the air ia the form of gas. This is easily effected in the 

 following manner. When a greenhouse or hothouse is shut up, warm 



