f travel, while an innumerable host of others occasionally make
use of it, although it may seem from their structure and place of
growth that they were made especially to be transported by the wind
or by some animal. As has been seen in examples previously mentioned,
one portion of a plant is transported in one way, and another portion
by one or two other methods.

[Illustration: FIG. 13.--Branch of loosestrife bearing tuber
bulblets.]

[Illustration: FIG. 14.--One of the tubers enlarged.]

13. Seeds and fruits as boats and rafts.--An excellent place in which
to begin investigating this part of the subject is to pay a visit
to the flats of a creek or river late in autumn or in the spring,
after the water has retired to its narrow channel, and examine piece
after piece of the rubbish that has been lodged here and there against
a knoll or some willows, a patch of rushes or dead grass. We are
studying the different modes by which plants travel. In the driftwood
may be found dry fruits of the bladder nut, brown and light, an inch
and a half in diameter. See how tough they are; they seem to be
perfectly tight, and even if one happens to have a hole punched in
its side, there are probably two cells that are still tight, for there
are three in all. Within are a few seeds, hard and smooth. Why are
they so hard? Will it not be difficult for such seeds to get moist
enough and soft enough to enable them to germinate? The hard coats
enable the seeds to remain uninjured for a long time in the water,
in case one or two cells of the papery pods are broken open; and after
the tough pod has decayed and the seeds have sunken to the moist earth
among the sticks and dead leaves, they can have all the time they
need for the slow decay of their armor. Sooner or later a tiny plant
is likely to appear and produce a beautiful bush. Engineers are
boasting of their steel ships as safe and not likely to sink, because
there are several compartments each in itself water-tight. In case
of accident to one or two chambers, the one or two remaining tight
will still float the whole and save the passengers.

[Illustration: FIG. 15.--Fruit of bladder nut with three tight
cells.]

I wonder if the engineers have not been studying the fruit of the
bladder nut? But this is not all. Many of the dry nuts hang on all
winter, or for a part of it, rattling in the wind, as though loath
to leave. Some of them are torn loose, and in winter there will be
a bette