Planta

Plants

Plantain-eaters, or Turacos, a family of
birds (Musophagidoe) peculiar to Africa. The
coloring is usually metallic blue or green,
aften varied with crimson; the red feathers
contain a peculiar soluble pigment called tu-
racin.

Plantain.
i, Single flower; 2, germen.

Plantin, Christophe (c. 1514-80), French
printer, born at St. Avertin, near Tours; es-
tablished at Antwerp one of the largest print-
ing-houses in Europe. His greatest work is
the Antwerp Polyglot Bible (8 vols. 1569-
73). He was also the owner of printing-houses
at Paris and Leyden. In 1876 his Antwerp
printing-house, together with its collections,
was opened as the Musee Plantin.

Plant-lice. See Aphids,

Plants, the term broadly applied to living
organisms endowed with vegetable life in
contrast to animal life, in general non-sen-
tient. The chief purpose served by plants is
the provision of food for the whole animal
world. Moreover, the part they play in the
interchange of gases renders the air fit to be
breathed by animals, which in return ttfve off
carbon dioxide utilized for plant food. Prac-
tically the whole surface of the earth is cov-
ered with vegetation of one kind or another,
irom the giants of the forests to the herbage

of the meadows, the lowly desert plant and
the lichen of the rock.

Plant physiology i? concerned with the
functions necessary for the well-being of the
individual and the propagation of the species.
These may be looked on as forming a cycle,
of which movement, growth, respiration, nu-
trition, and reproduction are the important
stages in the higher plants, and constitute the
life-history of those that consist of a single
cell. In the lowest plants there is a certain
amount of locomotion. In diatoms and cles-
mids progress through the water is effected
by means of protruaile threads of proto-
plasm thrust through the cell wall. Helio-
tropism, or the action of light on vegetable
lifr, may be observed in window plants, the
stems of which bend toward the window,
while the leaves assume a position at right
angles to the light. On the other hand, the
tendrils of the vine and Virginia creeper turn
away from the light. To gravitation is due
the downward growth of primary roots and
the horizontal growth of lateral branches.

The simplest plants consist of single cells,
and the higher plants originate as single cells,
and growth is carried on by cell division and
specialization. The former takes place at the
growing points above and below, except in
the case of the lateral roots, which arise at
some distance from the tip, where the tissues
have already begun to differentiate. The next
phase is that of elongation, due to surface
growth in the cell wall, and the distension of
the cell by the absorption of water. Internal
organs are developed by the fusion of cell

Knight's Experiment, showing
that the normal direction oj
root and stem is due to gravity.

cavities and the thickening of cell walls; and
periodicity of growth may be observed cor-
responding to the alternations of day and
night and of the seasons with their periodical
changes of light and temperature, Growth is
most rapid in spring, after the retardation of