from the lower end of which the root grew, partakes of the thickening,
perhaps also some joints of stem above: so the bud-bearing and growing
top is stem.

[Illustration: Fig. 86. Sweet-Potato plant forming thickened roots. Some
in the middle are just beginning to thicken; one at the left has grown
more; one at the right is still larger.]

[Illustration: Fig. 87. Fascicled fusiform roots of a Dahlia: _a_, _a_,
buds on base of stem.]

77. A fine example of secondary roots (67), some of which remain fibrous
for absorption, while a few thicken and store up food for the next
season's growth, is furnished by the Sweet Potato (Fig. 86). As stated
above, these are used for propagation by cuttings; for any part will
produce adventitious buds and shoots. The Dahlia produces _fascicled_
(i. e. clustered) fusiform roots of the same kind, at the base of the
stem (Fig. 87): but these, like most roots, do not produce adventitious
buds. The buds by which Dahlias are propagated belong to the surviving
base of the stem above.

78. =Anomalous Roots=, as they may be called, are those which subserve
other uses than absorption, food-storing, and fixing the plant to the
soil.

_Aerial Roots_, i. e. those that strike from stems in the open air, are
common in moist and warm climates, as in the Mangrove which reaches the
coast of Florida, the Banyan, and, less strikingly, in some herbaceous
plants, such as Sugar Cane, and even in Indian Corn. Such roots reach
the ground at length, or tend to do so.

_Aerial Rootlets_ are abundantly produced by many climbing plants, such
as the Ivy, Poison Ivy, Trumpet Creeper, etc., springing from the side
of stems, which they fasten to trunks of trees, walls, or other
supports. These are used by the plant for climbing.

[Illustration: Fig. 88. Epiphytes of Florida and Georgia, viz.,
Epidendrum conopseum, a small Orchid, and Tillandsia usneoides, the
so-called Long Moss or Black Moss, which is no moss, but a flowering
plant, also _T. recurvata_; on a bough of Live Oak.]

79. =Epiphytes, or Air-Plants= (Fig. 88), are called by the former name
because commonly growing upon the trunks or limbs of other plants; by
the latter because, having no connection with the soil, they must derive
their sustenance from the air only. They have aerial roots, which do not
reach the ground, but are used to fix the plant to the surface upon
which the plant grows: they also take a part in absorbing moisture from
the air.