THE INTERNAL STRUCTURES OF PLANTS. 197 



When the cells of cellular tissue, or parenchyma, 

 are crowded, they may fit exactly against each other, 

 and leave no unoccupied spaces (Fig. 357). We have 

 then complete parenchyma. 



When the walls of cellular tissue are round, so 

 that spaces are left between the points of contact 



FIG. 857. FIG. 858. 



(Fig. 358), the tissue is called incomplete parenchyma. 

 The spaces between the cells in incomplete paren- 

 chyma are called intercellular spaces. Lacunes are 

 formed when an intercellular space is produced by 

 the destruction of cells from any cause. 



EXERCISE LXIII. 

 Structure and Production of Cells. 



EXPERIMENT. Apply a weak tincture of iodine to 

 a little of the green tissue of a leaf, or other succu- 

 lent vegetable matter. The contents of the cells are 

 first colored brown^and presently they shrink away 



