Encyclopedia Britannica 1963 [18].pdf

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ENCYCLOPEDIA
BRITANNICA
THE
UNIVERSITY O F CHICAGO
The Encyclopadid Britaanica
ir
ptlblished with the editoridl advice ofthe factllties
of The University of Chicago and of a
committee of members of the faczllties of Oxford, Cambridge
and
of
a committee
and Londolz tlni~ersities
at The University
of
Tovonto
"
LET
K
N
O
W
LED
G
E
G
R
O
W
FRO M M
O
RE
T
O
M
O
RE
AND THUS BE HUMAN LIFE
E
N
RI
C
HE
D
."
A
New
Sa~vey U n i v e ~ ~ d
of
Klzowled'ge
Volume
18
P
LANTS
TO
R
AYMUND
OF
T
RIPOLI
E N C Y C L O P E D I A
BRITANNICA, INC.
W I L L I A M B E N T O N , PUBLISHER
CHICAGO
LONDON
TORONTO
GENEVA
SYDNEY
PRINTED
IN
THE
U.
S.
A.
FOUNDED
(organisms) are commonly divided into two general
groups-the animal kingdom and the plant kingdom.
With higher organisms the difference between plants and
animals is quite obvious: it is simple, indeed, to dis-
tinguish seaweed. ferns and trees from fish, birds and man How-
ever, in the case of the lower forms of life-bacteria, fungi, slime
molds, protozoa. sponges-the distinction often is not so evident,
and indeed, it is an artificial one since plants and animals probably
had common ancestors in evolution (see A
NIMAL
).
The biologist recognizes no definite line separating animals and
plants, or for that matter separating life and nonlife (see V
IRUSES
).
But on the basis of certain fundamental differences in
(1)
mode
of nutrition;
( 2 )
scheme of growth;
(3)
cell wall composition;
and
(4)
locomotion, higher organisms may be placed in either
the animal kingdom or in the plant kingdom.
1.
Plants generally manufacture their own food, a process (see
Photosyntheszs below) directly associated with the presence in
plant cells of tiny bodies or plastids containing chlorophyll, a vital
green pigment. Animals, on the other hand, generally lack chloro-
phyll and are unable to manufacture their own food; they depend
ultimately upon plants for food.
2.
Embryonic tissues remain extremely active in plants and re-
sult in what is termed unlimited growth; as tissue dies it l e -
mains in place and the young, active tissue grows away from it
Thus each apex of the root or shoot system consists of an aggre-
gation of embryonic cells, an apical meristem, which persists
throughout the life of the plant unless it changes into a repro-
ductive cone or flower, or is destroyed by accident or disease; in
some higher plants, especially treelike forms, lateral meristems
(vascular and cork cambia) produce a growth in girth (see
Tissues below). A mature animal, however. usually attains a
maximum size and a characteristic form, that is, it has a limited
growth pattern.
3.
Almost all plants have cells whose walls contain cellulose
and are, therefore, more or less rigid. Animal cells generally
lack cellulose, and their ceIl walls are usually elastic.
4.
Higher plants are anchored to the soil or to some other solid
surface from which they cannot move by their own power. Most
n
P
LANTS
Volume
18
T
O
RAYMUND
T
RIPOLI
OF
ment and make rather rapid changes to new locations when this is
necessary.
Of course there exist plantlike animals such as the sessile marine
corals, graptolites, anemones, sponges; and there exist also ani-
mallike plants such as bacteria, fungi and certain stages of algae
and of higher plants. Nevertheless, nhen all characteristics are
considered, it is relatively easy to determine whether an organ-
ism should be listed as a plant or as an animal. For the really
difficult cases-slime molds, euglenoids, chlamydomonads, etc.-
some biologists have advocated a separate kingdom, the protista
(see P
ROTOZOA
).
This article is divided into the following sections:
I.
Classification of Plants
1.
Cr>ptogams
2 .
Phaneropams
11.
Morphology of Plants
1
Alternation of Generations
2 .
Plant Body
111.
Anatomy
of
Plants
A. Minute Structure
1.
The Cell
2.
Cell Types and Tissues
B. Organization
of
the Plant Body
1.
Nonvascular Plants
2 .
Vascular Plants
C. Tissues
1.
Meristems
2 .
The Primary Plant Body
3.
Epidermis
4.
Cortex
5.
Mesophyll
6.
Vascular System
7.
Laticiferous Tissue
8.
Cambium and Secondary Growth
9.
Secondary Vascular Tlssues
10.
Phellogen and Periderm
IV.
Plant Physiology
A. Physiology of the Plant Cell
1.
Organization
of
the Plant Cell
2.
Protoplasm
3.
Permeability
4.
Osmotic Relations
5.
Plasmolysis
6.
Enzymes
LANTS AND PLANT SCIENCE.
Living things animals, on the other hand, are capable of considerable move-

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