r chance than at any other time for the wind to do the seeds
a favor, especially when there is snow on the ground, for then they
will bound along before the breeze till something interrupts them.

Here among the rubbish are some shriveled wild grapes also. As we
shall see elsewhere, their best scheme is to be eaten by certain birds,
which do not digest their bony seeds; but in case some of them are
left there is another mode of travel, not by wings of a bird, but
by floating on water.

[Illustration: FIG. 16.--Shriveled wild grapes overlooked by birds,
now ready to float on water, and a clean seed not able to float.]

Clean grape seeds sink at once, but covered by the dry skin and pulp,
they float. In a similar manner the dry seeds of several dogwoods
are eaten for the pulp by birds, but in case any are left they behave
after the manner of grapes.

14. Bits of cork around the seeds prevent them from
sinking.--Narrow-leaved dock is a prominent weed, and is especially
at home on river bottoms and on low land that is flooded once in a
while.

[Illustration: FIG. 17.--Fruit and adherent calyx of narrow-leaved
dock; a cross section and a naked, seed-like fruit (enlarged).]

Did you ever wonder what could be the object of a round, spongy
tubercle on the outside of each of these sepals which hold the ripened
seed closely? I did not know their use for a long time, but now think
I have discovered their meaning. They are not exactly life-preservers,
but the next thing to it. The naked, seed-like fruit, the shape of
the fruit of buckwheat, sinks at once when free from everything else,
but with the dry calyx still attached, it floats with the stream.

15. An air-tight sack buoys up seeds.--Here are several dry fruits
of sedges--plants looking considerably like grasses. There are a good
many kinds, and most of them grow in wet places. The seed-like fruit
of those we examine are surrounded each by a sack which is considerably
too large for it, as one would be likely to say, but in reality it
serves to buoy the denser portion within, much after the plan of the
bladder nut. In some instances the sack is rather small, but a corky
growth below the grain helps to buoy it on water.

[Illustration: FIG. 18.--Fruit of Asa-Gray sedge with an inflated
sack about it.]

Sedges that grow on dry land usually have the sack fitted closely,
instead of inflated, and the whole mass sinks readily in water. Now
we see the probable reason why t