CHAPTER II 



Cell Organs^ The Nucleus^ Mitochondria 

 and Golgi Apparatus 



IN discussing the cell-theory it was concluded that the 

 only satisfactory general description of a cell is "a 

 nucleated portion of protoplasm," and this description or 

 definition indicates the important part played by the 

 nucleus in the life of the cell. It is not the purpose of this 

 book to discuss at all fully the problems of cell-physiology, 

 but it may not be out of place to say a few words on the 

 function of the nucleus. The nucleus seems to act as the 

 centre which controls the metabolic activities of the cell;. a 

 non-nucleated portion of protoplasm can neither absorb 

 nourishment nor secrete. If a ciliated Protozoon is cut in 

 two, in such a way that one half contains the nucleus, the 

 nucleated portion can regenerate or repair the missing part, 

 but the half which lacks any nuclear matter is unable to 

 repair the wound. The cilia continue to move for a time, 

 so that the power of locomotion remains, and it may engulf 

 food, but since the food is not digested and no regeneration 

 takes place, it soon dies. Again, it has been shown that the 

 nucleus is necessary for the secretion of a cell-wall in the 

 plant cell by an ingenious experiment of TOWNSEND. He 

 placed root-hairs of Marchantia in hypertonic solution of 

 salt so that plasmolysis took place, i.e. owing to the with- 

 drawal of fluid from the vacuole by osmosis, the protoplasm 

 was drawn away from the cell-wall and became aggregated 

 into naked masses. Some of these masses were nucleated, 

 some were without nuclei but were connected by fine strands 



