24 



Elementary Botany 



When cell division is about to take place, two nuclei are formed 

 either by the division of the original one, or by its disappearance, 

 and the formation of two fresh ones. 



The whole mass of the protoplasm now aggregates around 

 these nuclei, and a cell wall is formed between the masses thus 

 produced, growing inwards from the circumference to the centre, 

 thus dividing the mother cell into two daughter cells, each of 

 which may grow to the size of the mother cell, and itself undergo 

 division. The formation of reproductive cells we shall have 

 to notice later on (page 117). 



Except in a few cases, cells do not remain through life 

 individually separate, but ai-e united together to form ' tissues.' 



These may be grouped accord- 

 ing to either their function, or 

 their structure. Under the for- 

 mer method of division we have 

 two kinds, viz. meristem, which 

 is a tissue where the cells remain 

 vitally active and capable of di- 

 vision, and permanent tissue, 

 where the cells are no longer 

 able to divide. If we arrange 

 them according to their struc- 

 ture, we distinguish those tissues 

 which consist of elongated cells 

 overlapping one another, and 

 which are known as prosenchy- 

 ma, and those which are formed 

 of shorter cells placed end to 

 end, or parenchyma. These 

 '■'.■; 41— Cells of stem of ;7c/« /^aja. two forms of tissucs, however, 



Mtristem cells in process of division ; A-, . 



nucleus ; dividing, a ; fully divided, i. paSS the One into the Other bv 



(.After Prantl.) * „ , . ■' 



endless gradations. 

 Sometimes the term sclerenchyma is used to denote either 

 prosenchymatous or parenchymatous tissues, where the walls 

 of the cells have become very thick and hard, and often dark 

 coloured. 



