TISSUES AND ORGANS 



47 



M 



^-L - nucleus-. . -Tr^ 



...^excuote 



ceTl membrane- 



i) 



Onion cells and epithelial cells, 

 these plant and animal cells alike ? 

 they different? 



In what ways are 

 In what wavs are 



In living Elodea, an interesting phenomenon may be observed. 



The protoplasm in the cell body is seen to be constantly in motion, 



flowing slowly in the direc- 

 tion of the arrows shown 



in the diagram. This 



streaming of protoplasm is 



one of the manifestations 



of life within the cell. In 



many cells this movement 



may be observed, and we 



have reason to believe that 



the protoplasm in most 



living cells is in motion, 



thus affording a circulation 



of the cell contents. 

 Tissues and organs. The 



cells which form certain 



parts of the veins, the flat 



blade, or other portions of a leaf, are found in groups or aggrega- 

 tions, and are more or less alike in size and shape. Such a 



collection of cells is called a tissue. Examples of tissues in ani- 

 mals are the cells 

 covering the outside 

 of the body, forming 

 the skin or epidermal 

 tissue ; muscle tis- 

 sue, which produces 

 movement; and 

 bony tissue, winch 

 forms the framework 

 to which the muscles 

 are attached. Tissue 

 Explain ce Us often differ 

 greatly in size and 



shape. A large plant or animal is ordinarily made up of more, 



not larger, cells than a smaller organism. 



Collections of tissues winch act together in the performance of 



Cells, tissues, and organs in plants and animals. 



this illustration. 



