CHAPTER II 



THE TISSUES OF PLANTS 



HISTOLOGY 



36. In many groups of plants a single cell makes up 

 the whole plant. In such groups the cells may vary 

 considerably in different species but there is not possible 

 a differentiation into cells of different structure for differ- 

 ent functions. All of the normal activities of the plant 

 are carried on by the same cell and, therefore, the modi- 

 fications of the cell are limited to those that do not inter- 

 fere with any of these functions. Aside from these 

 limitations the cell may vary much in size, shape, struc- 

 ture of wall, location and size of nucleus and vacuoles, 

 etc. 



37. In other forms of plants there are several to many 

 cells forming one plant in which all of the cells are 

 essentially alike and each capable of continued existence 

 by itself even if the others should be destroyed. Such a 

 plant is scarcely more than a group of nearly independent 

 individuals. As we study the more and more complex 

 forms of plants, however, we find that the cells are no 

 longer all alike or nearly so, but that some are different 

 from the others in shape, structure and function. The 

 cells are not all equivalent, the plant is not now a collec- 

 tion of nearly independent individual parts (cells) ))ut 

 the whole must be considered as an individual made up 

 of numerous differentiated parts. It is true that in the 

 history of every plant there occurs a one-celled stage and 



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