90 BOTANY FOR BEGINNERS CHAP. 



The parent cell contains a nucleus, which, as before divides 

 into two, and each part again divides, and thus there are four 

 nuclei in the cell. The protoplasm now divides into four masses 

 and each portion arranges itself around a nucleus. Each 

 rounded portion of protoplasm produces a new cell-wall and the 

 mother wall disappears, liberating the four cells. This method 

 of cell formation is called free-cell formation, and it only 

 takes place in reproductive organs. 



SUMMARY 



The Cell. All parts of plants are built up of microscopic elements 

 called cells, which may be living or dead. 

 The Structure of a Cell. Each living cell consists of 



(1) The cell-ivall, built up of cellulose. 



(2) The protoplasm , which lines the cell-wall. 



(3) The nucleus^ a denser portion of the protoplasm. 



Changes which the Cell- wall undergoes. It may become (i) 

 Cuticularised, (2) Lignified, (3) Mucilaginous. 



Protoplasm. The protoplasm is the living portion of the cell. It 

 contains the elements carbon, hydrogen, oxygen, nitrogen, and sulphur. 

 Protoplasm possesses the power of movement. It may rotate or 

 circulate. 



The Nucleus. All cells possess a nucleus, and in it a mtclcolus may 

 be present. It is built up of protoplasm, and contains a large quantity 

 of phosphorus. 



The Contents of the Cell. The cell may contain 



Cell-sap. Starch grains. 



Chloroplasts. Aleurone grains. 



Leucoplasts. 

 Chromoplasts. 



Fats. 



Crystals. 



Chloroplasts are masses of protoplasm containing a green colouring 

 matter called chlorophyll. The conditions necessary for the production 

 of chlorophyll are 



1 i ) A certain intensity of light. 



(2) A temperature above the freezing point. 



(3) A small quantity of iron in the food. 

 The functions of the Chloroplasts are 



1 i ) To absorb carbon dioxide from the air. 



(2) To split up the carbon dioxide into carbon and oxygen. 



(3) To form starch from sugar. 



Leucoplasts are masses of colourless protoplasm. They form starch 

 in those parts of the plants not exposed to light. 



Chromoplasts are masses of protoplasm saturated with other colouring 

 matter than chlorophyll. 



Starch Grains are formed (i) by chloroplasts in organs exposed to 



