CHAPTER II. 

 CELL-CONTENTS AND FORMS OF CELLS. 



A TYPICAL living cell may be said to consist of a wall and a 

 protoplast (a unit of protoplasm), although it is often customary 

 to refer to the protoplast alone as constituting the cell. This is in 

 view of the fact that the protoplasm which makes up the sub- 

 stance of the protoplast is the living substance of the plant. 



Besides the protoplasm other substances are also found in the 

 cell, hence in a general w^ay the cell may be said to be composed 

 of a wall and contents (cell-contents). The wall, as well as the 

 cell-contents, consists of a number of substances, and, as the cell- 

 contents are of primary importance in the development of the 

 plant, their nature and composition will be considered first. 



Cell-contents. — With the distinction already made the cell- 

 contents may be grouped into two classes: (i) Protoplasmic, or 

 those in which the life-processes of the plant, or cell, are mani- 

 fested ; and (2) non-protoplasmic, or those which are the direct or 

 indirect products of the protoplast. The first class includes the 

 protoplasm with its various dififerentiated parts, and the second, 

 the various carbohydrates (starches and sugars), calcium oxalate, 

 aleurone, tannin, oil, and a number of other substances. 



PROTOPLASMIC CELL-CONTENTS. 



Protoplasm. — Protoplasm occurs as a more or less semi- 

 fluid, slimy, granular, or foam-like substance, which lies close to 

 the walls of the cell as a relatively thin layer and surrounding a 

 large central cavity or vacuole filled with cell-sap, or it may be 

 distributed in the form of threads or bands forming a kind of net- 

 work enclosing smaller vacuoles. Protoplasm consists of two 

 comparatively well differentiated portions: (i) Certain more or 

 less distinct bodies which appear to have particular functions and 

 to which a great deal of study has been given, as the nucleus and 

 plastids; and (2) a less dense portion which may be looked upon 

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