PLANTS AND ANIMALS DISTINGUISHED. 23 



an ovum. This cell contains a serai-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, arid 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 Confervas 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 



