£72 
MOTIONS IN PLANTS. 
well worth attending to ; the flowers are so infinitely the most 
susceptible instruments j not a change of moisture but they 
indicate it before the quicksilver can move j not an increase 
of cold but the corolla will signify it. For the flower, in its 
extremely delicate mechanism, keeps pace with the variation, 
while our instruments only follow it. But the corolla may be 
said to obey the massy vapours j for it alters with them, and 
will not only indic.ste the sun’s concealment, but sometimes the 
passing over of each fleecy cloud. In watching a milkwart, I 
have seen it put on and off its little cap three times in half an 
F.tfpctof a hour; and it is curious, before a thunder storm, to go round 
thundei Sturm. your microscope, and see the preparation your whole gar- 
den makes for it, w'hile our instruments alter not till its effect 
has teen impressed on the air, and has produced a general 
change. But the most ext.'aordinary variation of the spiral 
wire alone is shown in or preceding them. Its univer- 
sal and continual trembling at this time, must have some cause 
well worth inquiring into it has always, indeed, been one of 
the strongest reasons with me for attributing its chief manage- 
Ellcctof great jj)oot to moisture. In a great flood last spring, in three days 
the water rose to a prodigious height, so as to endanger one 
On the spiral whole street in the suburbs of Exeter. At tliis time I placed 
under my eye a quantity of spiral wire taken from a geranium, 
and fixed it in my compound microscope ; its constant trem- 
bling attracted my attention, and made me watch it very ex- 
actly. This agitation lasted a whole day ; it was never still a 
single moment while I observed it, which I did conlinunlly ; 
and its elongations and contractions were accompanied with 
starts which involuntarily made me imitate it. It was then. 
Effect of the that I first observed the strong effect of a flood on the 
barometer, barometer. Mine is of the clock kind, and, I believe, a very' 
good one. Three times in three days it rose from 28” 30' to 
29® 33', and its quickest motion admirably tallied with the most 
hasty movement of the spiral wire. Surely, it is iiardly pos- 
sible to bring a stronger confirmation that both are directed by 
Iffect on the the same cause, and managed by the same powers. The fold- 
cuiu.la. corolla also appear to me strong proofs of this truth. 
