PLANTS AND ANIMALS DISTINGUISHED. 
23 
an ovum. This cell contains a semi-fluid, called proto¬ 
plasm, similar in composition and in function. In the 
very simplest forms the protoplasm is not enclosed by a 
membrane, but generally there is a cell-wall. In plants, 
with few exceptions, this wall is of cellulose, a substance 
akin to starch; in animals, with few exceptions, the wall 
is a pellicle of firmer protoplasm, i. e., albuminous. 
(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, dextrine, and starch; 
while animals are mainly made up of albumen, fibrine, 
and gelatine; 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 
both have no fixed shape. The spores of Confervse can 
hardly be distinguished from animalcules; the compound 
and fixed animals, Sea-mat and Sea-moss (Polyzoa), and 
Corals, often resemble vegetable forms, although in struct¬ 
ure 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 
