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TEXTBOOK OF BOTANY 



similar it is because their protoplasms are similar, ( 5 ) that when plants 

 develop or behave differently in the same environment it is because their 

 protoplasms are unlike, and (6) that life is a recognized property of a 

 very complex physical-chemical (colloidal) system. 



Parts of the cell. As shown in Fig. 30, the essential parts of the cell 

 may be outlined as follows: 



1. The protoplasm, differentiated into cytoplasm, plastids, and 

 nucleus, 



2. The vacuole — a cavity within the cytoplasm filled with water con- 

 taining sugars, salts, acids, and other substances largely in solution. 



3. The cell wall — a more or less complete covering around the proto- 

 plasm. Fine strands of protoplasm sometimes extend through the 

 wall from one cell to another. 



cell wall 



j^ 1^ r\ucleas ' 



cytoplasm 



protoplasm 



vacuole 



Fig. 30. Plant cells as seen through a microscope: A, a meristematic cell com- 

 posed of a nucleus and cytoplasm surrounded by a cell wall; B, an older cell which 

 has become enlarged by growth of the cell wall and the formation of a large central 

 vacuole; C, cell B as seen in perspective; D, starch grains formed in plastids in a 

 cell of a potato tuber; E, chloroplasts in a cell of a moss leaf. 



In order to appreciate protoplasm as the medium in which the numer- 

 ous chemical and physical processes of the cell occur, it will be neces- 

 sary to digress for a moment and consider some of the properties of 

 different states of matter. You have seen solid crystals of sugar and salt 

 disappear as they dissolved in water. You are also familiar with gelatin 

 and fruit jellies in which organic matter is dispersed in water without 

 being dissolved. Protoplasm seen through the microscope resembles a 

 jelly more than a solution. 



The solid, liquid, and gaseous states of matter are familiar to every- 



