way they contrive it, in either case.

[Illustration: FIG. 20.]

Among the many forms taken by the Arethusan leaf, one of the commonest is
long and gradually tapering,--much broader at the base than the point. We
will take such an one for examination, and suppose that it is growing on
the ground as in Fig. 20, with a root to its every fibre. Cut out a piece
of strong paper roughly into the shape of this Arethusan leaf, a, Fig. 21.
Now suppose the next young leaf has to spring out of the front of this one,
at about the middle of its height. Give it two nicks with the scissors at b
b; then roll up the lower part into a cylinder, (it will overlap a good
deal at the bottom,) and tie it fast with a fine thread: so, you will get
the form at c. Then bend the top of it back, so that, seen sideways, it
appears as at d, and you see you have made quite a little flower-pot to
plant your {158} new leaf in, and perhaps it may occur to you that you have
seen something like this before. Now make another, a little less wide, but
with the part for the cylinder twice as long, roll it up in the same way,
and slip it inside the other, with the flat part turned the other way, e.
Surely this reminds you now of something you have seen? Or must I draw the
something (Fig. 22)?

[Illustration: FIG. 21.]

6. All grasses are thus constructed, and have their leaves set thus,
opposite, on the sides of their tubular stems, alternately, as they ascend.
But in most of them there is also a peculiar construction, by which, at the
base of the sheath, or enclosing tube, each leaf articulates itself with
the rest of the stem at a ringed knot, or joint. {159}

[Illustration: FIG. 22.]

Before examining these, remember there are mainly two sorts of joints in
the framework of the bodies of animals. One is that in which the bone is
thick at the joints and thin between them, (see the bone of the next
chicken leg you eat), the other is that of animals that have shells or
horny coats, in which characteristically the shell is thin at the joints,
and thick between them (look at the next lobster's claw you can see,
without eating). You know, also, that though the crustaceous are titled
only from their crusts, the name 'insect' is given to the whole insect
tribe, because they are farther jointed almost into _sect_ions: it is
easily remembered, also, that the projecting joint means strength and
elasticity in the creature, and that all its limbs are useful to it, an