PLANTS AND ANIMALS DISTINGUISHED. 23 



This cell consists mainly of a semi-fluid substance called 

 protoplasm. In the very simplest forms the protoplasin 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. e., 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 quaternar}'', 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 

 fiBsh- 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 Confervae 

 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 frou) 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 



