ly serves
another good turn besides enabling them to adhere to animals. The
slime holds them to the spot where they are to grow, or it enables
some to float or to sink in water, according to the amount of the
mucilage.

46. Three devices of Virginia knotweed.--A perennial plant, four to
five feet high, grows on low land, usually in the shade. It is
_Polygonum Virginicum_, and so far without a common name, unless
Virginia knotweed be satisfactory. It is a near relative of knot grass
and smartweed and Prince's feather. The small flowers are borne on
a long, elastic, and rather stiff stem, and each flower stalk has
a joint just at the base. As this fruit matures, the joint becomes
very easy to separate. It dries with a tension, so that, if touched,
the fruit goes with a snap and a bound for several feet. The shaking
produced by the wind jostling several against each other is
sufficient to send off a number of ripe fruits in every direction.
Like many other plants we have seen, this has more than one way of
scattering seeds, and often more than two ways. Observe the slender,
stiff beak, terminating in two recurved points. Let a person or some
animal pass into a patch of these plants, and at once numerous fruits
catch on wherever there is a chance, and some are shot upon or into
the fleeces of animals, there to find free transportation for
uncertain distances. Should there be a freshet, some of these fruits
will float; or, in case of shallow currents after a rain, some of
them are washed away from the parent plant. Any inquisitive person
cannot fail to be pleased if he experiment with the plant when the
fruit is ripe.

[Illustration: FIG. 55.--Fruit of Virginia knotweed ready to shoot
off when shaken, or to let go of stem and catch on to passing animal.]

47. Hooks rendered harmless till time of need.--There are a number
of rather weedy-looking herbs, common to woods or low land, known
as Avens, _Geum_. They are closely allied to cinquefoil, and all
belong to the rose family. The slender stiles above the seed-like
ovaries of some species of Avens are described as not jointed, but
straight and feathery, well adapted, as we might suppose, to be
scattered by the aid of wind; while others are spoken of as having,
when young, stiles jointed and bent near the middle. In ripening,
the lower part of the stile becomes much longer and stouter. When
a whole bunch of pistils has drawn all the nourishment possible, or
all that is ne