the Poisonous Gases on Vegetables. 147 



aif. The sulphuretted hydrogen acts differently. Two cubic 

 inches in 230 times their volume of air had no effect in twen- 

 ty-four hours. Four inches and a half in eighty volumes of 

 air caused no injury in twelve hours, but in twenty-four hours 

 several of the leaves, without being injured in colour, were 

 hanging down perpendicularly from the leaf-stalks and quite 

 flaccid ; and though the plant was then removed into the open 

 air the stem itself soon began also to droop and bend, and the 

 whole plant speedily fell over and died. When the effects of 

 a large quantity, such as six inches in sixty times their volume, 

 were carefully watched, it was remarked that the drooping be- 

 gan in ten hours at once from the leaf-stalks, and the leaves 

 themselves, except that they were flaccid, did not look un- 

 healthy. Not one plant recovered, any of whose leaves had 

 drooped before it was removed into the air. 



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 progres- 

 sive flaccidity of the leaves, — the bending of them at their 

 point of junction with the foot-stalk, and the subsequent bend- 

 ing 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. 



These phenomena, when compared with what was observed 

 in the instances of sulphurous and hydrochloric acid, would ap- 

 pear to establish, in relation to vegetable life, a distinction 

 among the poisonous gases nearly equivalent to the difference 

 existing between the effects of the Irritant and the Narcotic 

 poisons on animals. The gases which rank as irritants in re- 

 lation to animals seem to act locally on vegetables, destroying 

 first the parts least plentifully supplied with moisture. The 

 narcotic gases — including under that term those which act on 

 the nervous system of animals, destroy vegetable life by attack- 

 ing it throughout the whole plant at once. The former pro- 

 bably act by abstracting the moisture of the leaves, the latter 

 by some unknown influence on their vitality. The former 

 seem to have upon vegetables none of that sympathetic influence 



