26 
POPULAR SCIENCE REVIEW. 
according to the force of the blow, the whole series become folded 
together, the secondary leafstalks fold together like the ribs of 
a fan, and the common stalk drops by the side of the stem. 
After an interval, the plant recovers its equilibrium, and the 
original position of the leaf is restored. Similar movements 
occur at night, constituting “ the sleep ” of the plant. Some 
of the tropical species of Oxalis show similar phenomena. 
Unlike our common Oxalis (0. Acetosella), the plants in question 
have long pinnate leaves similar to those of the Mimosa puclica, 
and at the least irritation they close their leaflets as in the last 
named plant ; in some instances, however, raising the leaflets 
instead of depressing them. By the older botanical writers 
the Oxalis was known as the ‘‘ Herba sentiens and Rumphius, 
who gives a full description, as well as a figure of it, expresses 
his surprise that in Amboyna the plant should be so often found 
in exposed places, where it would seem most likely to be ex- 
posed to violence, adding, somewhat facetiously, that it is like 
a young lady who wishes to be looked at, but not to be touched I 
One quality was attributed to the Oxalis which, did it really 
possess such, would render the services of the “ Professors ” who 
undertake the delineation of character from an inspection of the 
handwriting superfluous. So chaste was the plant that its leaves 
collapsed in the presence of vice, and hence it was made, so runs 
the tale, to serve as a sort of test, to eliminate the good 
from the bad, to act as a love-philtre, and even to expurgate 
the guilty and render them as free from taint as itself. It is a 
pity the herb should have lost its virtues in these days ! 
This Oxalis sensitiva, probably in its native country the 
most amenable of all plants to external influences, is in this 
country quite, or nearly quite, destitute of the power of closing 
its leaflets when irritated; a circumstance that should not be 
overlooked when casting about .for the causes of the pheno- 
menon. Our common wood-sorrel has the power of depressing 
its leaflets at night and of raising them in the day; but does 
not seem to be sensitive to mechanical stimuli. 
The Fly-trap Dioncea is another of the best known of the 
sensitive plants. It is closely allied to our Sun-dews, Drosera, 
the leaves of which are also said to be endowed with a certain 
sensitiveness — so feeble, however, that but few have ever seen it. 
In the Dioncea the upper half of the leaf folds in halves, like a 
sheet of note paper when an insect happens to touch one or 
more of the hairs which beset its surface. A chevaux-de-frise 
of bristly points surrounds the margin of the leaf, so that the 
unlucky insect remains a prisoner till it dies. What possible 
object the plant has in thus catching flies, or what is the real 
purport of the peculiar movement, no one knows, though, as 
may be supposed, speculation of the wildest character has been 
indulged in concerning it. 
