80. =Parasitic Plants=, of which there are various kinds, strike their
roots, or what answer to roots, into the tissue of foster plants, or
form attachments with their surface, so as to prey upon their juices. Of
this sort is the Mistletoe, the seed of which germinates on the bough
where it falls or is left by birds; and the forming root penetrates the
bark and engrafts itself into the wood, to which it becomes united as
firmly as a natural branch to its parent stem; and indeed the parasite
lives just as if it were a branch of the tree it grows and feeds on. A
most common parasitic herb is the Dodder; which abounds in low grounds
in summer, and coils its long and slender, leafless, yellowish
stems--resembling tangled threads of yarn--round and round the stalks of
other plants; wherever they touch piercing the bark with minute and very
short rootlets in the form of suckers, which draw out the nourishing
juices of the plants laid hold of. Other parasitic plants, like the
Beech-drops and Pine-sap, fasten their roots under ground upon the roots
of neighboring plants, and rob them of their juices.

81. Some plants are partly parasitic; while most of their roots act in
the ordinary way, others make suckers at their tips which grow fast to
the roots of other plants and rob them of nourishment. Some of our
species of Gerardia do this (Fig. 89).

[Illustration: Fig. 89. Roots of Yellow Gerardia, some attached to and
feeding on the root of a Blueberry-bush.]

82. There are phanerogamous plants, like Monotropa or Indian Pipe, the
roots of which feed mainly on decaying vegetable matter in the soil.
These are SAPROPHYTES, and they imitate Mushrooms and other Fungi in
their mode of life.

83. =Duration of Roots, etc.= Roots are said to be either _annual_,
_biennial_, or _perennial_. As respects the first and second, these
terms may be applied either to the root or to the plant.

84. =Annuals=, as the name denotes, live for only one year, generally
for only a part of the year. They are of course herbs; they spring from
the seed, blossom, mature their fruit and seed, and then die, root and
all. Annuals of our temperate climates with severe winters start from
the seed in spring, and perish at or before autumn. Where the winter is
a moist and growing season and the summer is dry, _winter annuals_
prevail; their seeds germinate under autumn or winter rains, grow more
or less during winter, blossom, fructify, and perish in the follo