CHAP. VIII 



Vitality 129 



distinct shapes, others constantly change their form. They 

 move, indeed, by a kind of flowing ; one part of their body is 

 pushed out and a part on the farther side drawn in. Some 

 of these lowly creatures have skeletons or shells of lime or 

 of flint. Great numbers of these shells, when the little 

 inmates are dead, form beds of chalk and ooze. Now 

 all living creatures begin life in this way ; at first they 

 are tiny masses of a jelly-like translucent stuff. Each 

 mass gets a skin or surrounding wall ; if fed, it grows 

 larger, and a wall is built up inside it, making its house a 

 two-roomed one. This process goes on and on ; the whole 

 mass grows larger and larger, and becomes divided up into 

 a corresponding number of compartments. The chambers 

 are not quite separated ; there are always holes left in the 

 walls, through which strands of the jelly-like stuff pass, and 

 so all of them are connected. The divisions in each 

 separate kind of animal or plant take place in a special 

 way, until' at last the whole body is built up, with all its 

 peculiarities of form and internal arrangement. The cells 

 of an animal's body do not, however, form walls as definitely 

 as do those of plants. 



In an ordinary plant there are millions of those com- 

 partments ; they are called cells, from their likeness in 

 general appearance to the cells of a honeycomb ; and the 

 enclosed stuff that we have spoken of as jelly is called 

 protoplasm, because it is believed that the first living things 

 that were formed were little drops of jelly-like stuff, not 

 unlike that within the cells, or composing the animalcute in 

 water. Protoplasm, wherever it occurs, from the highest 

 to the lowest forms of life, is supposed to have, within 

 certain limits, a similarity of nature. 



In some plants the cells are large enough to be visible 



■ to the naked eye, but the cells of most plants and animals 



are so small that they can only be seen with a microscope. 



We can now give a complete answer to the question. 

 What parts of a tree are alive ? It is only the protoplasm 

 of the cells. The walls of the cells are more or less dead. 

 As the cells grow older and larger, and the walls become 

 thicker, the amount of protoplasm within gets relatively 



K 



