FUNCTION.] AMMONIA, ETC. 317 



Carbonic acid, well recognised as the principal subsistence of 

 plants, will kill them in doses not very considerably greater 

 than that proportion which nature provides ; and we our- 

 selves should perish under excessive quantities of even the 

 most nutritious of our daily food. 



The effects of ammonia were precisely similar to those of 

 sulphuretted hydrogen just related, except that after the leaves 

 drooped they became also somewhat shrivelled. The pro- 

 gressive flaccidity of the leaves, the bending of them at their 

 point of junction with the footstalk, and the subsequent 

 bending of the stem, the creeping, as it were, of the languor 

 and exhaustion from leaf to leaf, and then down the stem, 

 were very striking. Two inches of gas, in 230 volumes of 

 air, began to operate in ten hours. A larger quantity and 

 proportion seemed to operate more slowly. (Turner and 

 Christison.} 



Yet the carbonate of ammonia in moderate doses is one of 

 the most valuable of all manures, and is freely taken up by 

 the leaves of plants, not only without inconvenience, but with 

 visible advantage. 



Cyanogen appears allied to the two last gases in property, 

 but is more energetic. Two cubic inches, diluted with 230 

 times their volume of air, affected a mignonette plant in five 

 hours; half a cubic inch, in 700 volumes of air, affected 

 another in twelve hours ; and a third of a cubic inch, in 1700 

 volumes of air, affected another in twenty -four hours. The 

 leaves drooped from the stem without losing colour; and 

 removal into the air, after the drooping began, did not save 

 the plants. (Turner and Christison.} 



Carbonic oxide is also probably of the same class, but its 

 power is much inferior. Four cubic inches and a half, diluted 

 with 100 times their volume of air, had no effect in twenty- 

 four hours on a mignonette plant. Twenty-three cubic inches, 

 with five times their volume of air, appeared to have as little 

 effect in the same time ; but the plant began to droop when 

 it was removed from the jar, and could not be revived. 



