112 ANIMAL LIFE 



Such are the pitcher-plants and sun-dews, and Venus-fly- 

 traps, which catch insects and use them for food nutrition. 

 But there are many plants, the fungi, which are not green 

 that is, which do not possess chlorophyll, the substance 

 on which seems to depend the power to make organic 

 matter out of inorganic substances. These plants feed on 

 organic matter as animals do. The cells of plants (in their 

 young stages, at least) have a wall composed of a peculiar 

 carbohydrate substance called cellulose, and this cellulose 

 was for a long time believed not to occur in the body of 

 animals. But now it is known that certain sea-squirts 

 (Tunicata) possess cellulose. It is impossible to find any 

 set of characteristics, or even any one characteristic, which 

 is possessed only by plants or only by animals. But nearly 

 all of the many-celled plants and animals may be easily 

 distinguished by their general characteristics. The power 

 of breaking up carbonic-acid gas into carbon and oxygen 

 and assimilating the carbon thus obtained, the presence of 

 chlorophyll, and the cell walls formed of cellulose, are char- 

 acteristics constant in all typical plants. In addition, the 

 fixed life of plants, and their general use of inorganic sub- 

 stances for food instead of organic, are characteristics 

 readily observed and practically characteristic of many- 

 celled plants. When the thousands of kinds of one-celled 

 organisms are compared, however, it is often a matter of 

 great difficulty or of real impossibility to say whether a 

 given organism should be assigned to the plant kingdom 

 or to the animal kingdom. In general the distinctive 

 characters of plants are grouped around the loss of the 

 power of locomotion and related to or dependent upon it. 



67. Living organic matter and inorganic matter. It would 

 seem to be an easy matter to distinguish an organism that 

 is, a living animal or plant from an inorganic substance. It 

 is easy to distinguish a dove or a sunflower from stone, and 

 practically there never is any difficulty in making such dis- 

 tinctions. But when we try to define living organic matter, 



