PLANTS AND ANIMALS DISTINGUISHED. 
23 
This cell consists mainly of a semi-fluid substance called 
protoplasm. In the very simplest forms the protoplasm is 
not enclosed by a membrane or cell-wall. In most plants 
the cell-wall is present, and consists of cellulose, a sub¬ 
stance akin to starch; in animals, with few exceptions, 
the wall is a pellicle of firmer protoplasm, i. £., albumi¬ 
nous. 
(2) Composition.— Modern research has broken down the 
partition between plants and animals, so far as chemical 
nature is concerned. The vegetable fabric and secretions 
may be ternary or binary compounds; but the essential 
living parts of plants, as of animals, are quaternary, con¬ 
sisting of four elements—carbon, hydrogen, oxygen, and 
nitrogen. Cellulose (woody fibre), starch, and chlorophyl 
(green coloring matter) are eminently vegetable products, 
but not distinctive; for cellulose is wanting in some plants, 
as some Fungi, and present in some animals, as Tunicates; 
starch, under the name of glycogen, is found in the liver 
and brains of Mammals, and chlorophyl gives color to the 
fresh-water Polyp. Still, it holds good, generally, that 
plants consist mainly of cellulose, dextrin, and starch ; 
while animals are mainly made up of albumen, fibrin, and 
gelatin ; that nitrogen is more abundant in animal tissues, 
while in plants carbon is predominant. 
(3) Form.— No outline can be drawn which shall be com¬ 
mon to all animals or all plants. The lowest members of 
each group have no fixed shape. The spores, of Confervse 
can hardly be distinguished from animalcules; the com¬ 
pound and fixed animals, Sea-mat and Sea-moss (Polyzoa), 
and Corals, often resemble vegetable forms, although in 
structure widely removed from plants. Similar conditions 
of life are here accompanied by an external likeness. In 
free-living animals this resemblance is not found. 
(4) Structure. —A plant is the multiplication of the unit 
—a cell with a cellulose wall. Some simple animals have 
