CHAP. X. 
RESPIRATION. 
323 
air caused a yellowish green discolouration in an hour, and, 
drooping and withering in the course of twenty-four hours. 
The leaves were not acid on the surface." 
" The effects of sulphureted hydrogen are quite different 
from those of the acid gases. The latter attack the leaves at 
the tips first, and gradually extend their operation towards 
the leafstalks ; when in considerable proportion, their effects 
began in a few minutes; and if the quantity was not great, 
the parts not attacked generally survived, if the plants were 
removed into the air. The sulphureted hydrogen acts dif- 
ferently; two cubic inches in 230 times their volume of air 
had no effect in twenty-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 leafstalks, 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 began in ten hours, at once 
from the leafstalks; and the leaves themselves, except that 
they were flaccid, did not look unhealthy. 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 
sulphureted 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 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 pro- 
portion seemed to operate more slowly." 
" 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 
Y 2 
