COMPOSITION OF LIVING THINGS 



27 



But we may not know so much about their uses to the plant. Each 

 of these structures differs from every other part, and each has a 

 separate work or function to perform 

 for the plant. The root holds the plant 

 firmly in the ground and takes in water 

 and mineral matter from the soil; the 

 stem holds the leaves up to the light and 

 acts as a pathway for fluids between the 

 root and leaves; the leaves, under cer- 

 tain conditions, manufacture food for 

 the plant and breathe; the flowers form 

 the fruits; the fruits hold the seeds, 

 which in turn hold young plants which 

 are capable of reproducing adult plants 

 of the same kind. 



The Functions of an Animal. If 

 we examine the grasshopper more 

 carefully, we find that it has a head, 

 a jointed body composed of a middle 

 and a hind part, three pairs of jointed 

 legs, and two pairs of wings. Obvi- 

 ously, the wings and legs are used for movement; a careful 

 watching of the hind part of the animal shows us that breathing 

 movements are taking place; a bit of grass placed before it may 

 be eaten, the tiny black jaws biting little pieces out of the grass. 

 If disturbed, the insect hops away, and if we try to get it, it 

 jumps or flies away, evidently seeing us before we can grasp it. 

 Hundreds of little grasshoppers indicate that the grasshopper can 

 reproduce its own kind, but in other respects the animal seems 

 quite unlike the plant. The animal moves, breathes, feeds, and 

 has sensation, while apparently the plant does none of these. It 

 will be the purpose of later chapters to prove that the functions 

 of plants and animals are in many respects similar and that both 

 plants and animals breathe, feed, and reproduce. 



Organs. If we look carefully at the organ of a plant called a 

 leaf, we find that the materials of which it is composed do not ap- 

 pear to be everywhere the same. The leaf is much thinner and 

 more delicate in some parts than in others. Holding the flat, ex- 



Section through the blade of a 

 leaf, as seen under the com- 

 pound microscope ; *S, air 

 spaces, which communicate 

 with the outside air; V, vein 

 in cross section ; ST, breath- 

 ing hole ; E, outer layer of 

 cells; P, green cells. 



