196 THE SECOND BOOK OF BOTANY. 



In the same way prepare and examine slices of 

 melon, potato, cabbage-stalk, apple, orange-pulp, or 

 any ripe fruit, or succulent stem, or young, growing 

 shoot. 



Take a little of the pulp of boiled rhubarb on the 

 end of a needle, and put it upon a slip of glass, add- 

 ing a drop of water. Under the microscope you will 

 again see just such appearances as were presented by 

 the elder. Place thin petals under the microscope, 

 and observe their structure. 



These walled spaces, of varying shape, and of 

 about the same diameter in all directions, are called 

 cells, and the mass of substance they form by their 

 union is cellular tissue. 



Cells consist of an outer membrane, or wall, that 

 contains various liquid, semi-liquid, and solid matters. 

 They vary much in size. The largest cells of the 

 pith are -^ of an inch in diameter, though a cell 

 2^5- of an inch in diameter is a very large one. Those 

 of ordinary cellular tissue are about ^J-g- of an inch 

 in diameter. The very smallest vegetable cells are 

 from ^Vfr to -g-gVn- of an inch in diameter. The 

 shape of the cells of cellular tissue depends upon the 

 pressure around them. When there is no pressure, 

 they are round, or egg-shaped ; but, if they crowd 

 each other as growth goes on, they become many- 

 sided, or polyhedric. 



Cellular tissue is said to be regular when its cells 

 are cubical; prismatic, when they are elongated; 

 tabular, when they are flattened ; and muriform^ 

 whjen they look like courses of brick in a wall. All 

 cellular tissue, whatever the form of the cells, is 

 called parenchyma. 



