OF THE ATMOSPHERE OF HOT-HOUSES. 301 



as we have already seen, plays such an important part in the 

 progress of vegetable life. This gas, though composed of 

 hydrogen and nitrogen, is very unlike these, or, indeed, any 

 other gases with which the chemist is yet acquainted. It is 

 possessed of a most powerful penetrating smell, which is familiar 

 to almost every one as hartshorn and smelling-salts. In excess, 

 it suffocates living animals, though it requires a very considera- 

 ble preponderance in the atmospheric volume to destroy either 

 animal or vegetable life. Illustrations of this fact we have fre- 

 quently observed in fumigating a pit, or house, for the destruc- 

 tion of aphides, and other insects ; but it destroys both, much 

 more rapidly, when evolved at a high temperature, as we fre- 

 quently find it in hot-beds of dung, when plants have been 

 placed in them before the gas and heat had somewhat subsided, 

 as well as in vineries, which we have seen filled with ammoni- 

 acal gas, when the atmosphere was near 100 degrees, when the 

 edges of the tender leaves appeared as if they had been nipped 

 with frost, but the insects were not entirely destroyed. In 

 fumigating frames and pits with this and other gases, we have 

 seen some kinds of tender-leaved plants completely destroyed, 

 while many of the insects, tenacious of life, were uninjured, 

 which has fully satisfied me of the truth of the statement already 

 made, i. e., that the. generality of tender plants are more sensi- 

 tive of noxious gases than living animals, although few may be 

 inclined to believe it, and their disbelief is too often manifested 

 in the treatment their plants receive. There can be little doubt 

 that it is this gas, in a certain proportion of atmospheric air, 

 that produces the luxuriance of plants, when combined with the 

 mild heat of a dung-bed. Were we to ask a chemist, What are 

 the manures which, in a fluid or gaseous state, can in these 

 forms be presented to the atmosphere, and diffused among living 

 plants, in a hot-house ? he would answer, " Ammonia, obtain 

 it from whatever source you may, either in a simple or combined 

 state ;" and as hitherto our chief supply of this substance, which 

 we have had to deal with in the common operations of garden- 

 ing, has been found in our hot-beds of stable manure, resulting 

 from the decomposition of vegetable matter, principally the nitro- 

 geneous substances contained in corn and other matter on which 



