PLANTS AND ANIMALS. 



93 



reason, that some Protozoa divide and yet cohere, forming 

 loose colonies of cells. In these, there is little or no division 

 of labour ; we can hardly call them " bodies " ; yet they 

 consist of many cells in loose union. Such colonies are 

 found among some of the very simplest of the Protozoa, as 

 well as among Rhizopods, and among Infusorians. 



Plants and Animals. — Plants live a life fundamentally 

 similar to that of animals. Like animals, plants breathe 

 and digest, and they often move and feel ; the higher forms 

 are built up of many cells, and spring from a fertilised 

 egg-cell; the chemist finds many substances in plants, 

 which occur in animals also. 



Thus there is no absolute distinction between plants and 

 animals ; they represent divergent branches of a V-shaped 

 tree of life. It is easy to distinguish extremes, like bird 

 and daisy, less easy to contrast sponge and mushroom, well 

 nigh impossible to decide whether some very simple forms, 

 which Hseckel called "protists," have a bias towards plants 

 or towards animals. But the food which most plants absorb 

 is cruder or chemically simpler than that which animals are 

 able to utilise. Plants derive the carbon they require from 

 the carbonic acid gas of the air, whereas only a few green 

 animals have this power. Almost all animals depend on the 

 sugar, starch, and fat already made by other animals, or by 

 plants. As regards nitrogen, most plants derive this from 

 simple nitrates, absorbed along with water by the roots ; 

 whereas animals obtain their nitrogenous supplies from the 

 complex proteids formed within other organisms. Most 

 plants, therefore, feed at a lower chemical level than do 

 animals, and it is very characteristic of them, that in the 

 reduction of carbonic acid, and in the manufacture of starch 

 and proteids, the kinetic energy of sunlight is transformed 

 by the living matter into the potential chemical energy of 

 complex food-stuffs. Animals, on the other hand, get their 

 food ready-made; they take the pounds which plants have, 

 as it were, accumulated in pence, and they spend them. 

 For it is very characteristic of animals that they convert the 

 potential chemical energy of food-stuffs into the kinetic 

 energy of locomotion and other activities. In short, the 

 great distinction — an average one at best — is that most 

 animals are more active than most plants. But as the 



