CHAPTER VIII 



THE HISTOLOGY OF THE TISSUES 



Kinds of Cells. All cells can be classed according to their 

 shape into (a) Parenchyma, and (b) Prosenchyma. 



A parenchyma cell is one in which the diameter of the cell 

 is about the same in every direction. Cells of this description 

 are especially abundant in the succu- 

 lent parts of plants. The ground tissue 

 of a plant is composed of parenchyma 

 cells, and in many cases they form a 

 storehouse for reserve material, as in 

 the turnip. When such cells are very 

 numerous in an organ they are said to 

 form parenchymatous 

 tissue. 



A prosenchyma 

 cell is long and nar- 

 row. Cells of this 

 description may lose 

 their living contents 



and become filled with air and water. If a 

 number of prosenchyma cells are placed end-to- 

 end so that the transverse walls are at right 

 angles to the long side walls, the transverse 

 walls may become perforated, and so form a 

 vessel. The living contents of the cells be- 

 come absorbed after the transverse walls are 

 broken down, and eventually the fully formed vessels contain 

 only air or water. The markings on the walls of the vessels 

 supply the botanist with their characteristic names. 



FIG. 118. Parenchyma cell 

 from fruit of Bean. ( X 500.) 



FIG. no. Dia- 

 gram of Prosen- 

 chyma cell. 



