26 



BOTANY 



Protoplasm. — The living matter of which all cells are formed 

 is known as 'protoplasm (from two Greek words meaning first 

 form). 



The bulk of the nucleus is filled with a fluid; in some nuclei a 

 body known as a nucleolus is found; it does not seem to be a 

 constant structure. The protoplasm surrounding the nucleus is 



called cytoplasm be- 

 cause it makes up the 

 body of the cell. The 

 nucleus plays a very 

 important part in the 

 life of a cell. Cells 

 grow to a certain size 

 and then split into two 

 new cells. In this pro- 

 cess, which is of very 

 great importance in the 

 growth of both plants 

 and animals, the nu- 

 cleus divides first. The 

 chromosomes also divide, each splitting lengthwise so that an 

 equal number go to each of the two cells formed from the old 

 cell. Lastly, the cytoplasm separates and two new cells are 

 formed. This process is known as fission. It is the usual 

 method of growth found in the tissues of plants and animals. 



The protoplasm in some cells collects into little bodies called plastids. 

 In plant cells the plastids are frequently colored green. This green coloring 

 matter, which is found only in plant cells, is called chlorophyll and green 

 plastids are called chlorophyll bodies. The cytoplasm of a cell contains 

 spaces, which are usually filled with a fluid known as cell sap. These spaces 

 in the cytoplasm are given the name of vacuoles. Frequently non-living 

 materials are found within the cytoplasm of the cell. 



The cell is surrounded by a very delicate living structure called the cell 

 membrane. This is so thin that it is impossible to get a microscope of power 

 enough to throw any light on its structure. Outside this membrane a wall 

 is formed by the activity of the protoplasm in the cells of plants. In the 

 cells of the pith it was the wall of cellulose or wood that you saw under the 

 microscope. The wood used in building is made up of the dead walls of 

 plant cells. 



Stages in the division of one cell to form two cells. Note 

 the separation of the chromosomes in the nucleus. 

 Which part of the cell divides first ? 



