internode, and leaf. Thus it follows that stems must bear leaves. The
marked stems of seedlings show greater growth towards the top of the
growing phyton. It is only young stems that elongate throughout. The older
parts of a phyton grow little, and when the internode has attained a
certain length, variable for different stems and different conditions, it
does not elongate at all.

The root, on the contrary, grows only from a point just behind the tip.
The extreme tip consists of a sort of cap of hard tissue, called the
root-cap. Through a simple lens, or sometimes with the naked eye, it can
be distinguished in most of the roots of the seedlings, looking like a
transparent tip. "The root, whatever its origin in any case may be, grows
in length only in one way; namely, at a point just behind its very
tip. This growing point is usually protected by a peculiar cap, which
insinuates its way through the crevices of the soil. If roots should grow
as stems escaping from the bud-state do,--that is, throughout their whole
length--they would speedily become distorted. But, since they grow at the
protected tips, they can make their way through the interstices of soil,
which from its compactness would otherwise forbid their progress."[1]

[Footnote 1: Concerning a few Common Plants, p. 25.]

The third difference is that, while the stem bears leaves, and has buds
normally developed in their axils, roots bear no organs. The stem,
however, especially when wounded, may produce buds anywhere from the
surface of the bark, and these buds are called _adventitious_ buds. In the
same manner, roots occasionally produce buds, which grow up into leafy
shoots, as in the Apple and Poplar.[1]

[Footnote 1: See Gray's Structural Botany, p. 29.]