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 Conferva 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 



