234 



GENERAL MORPHOLOGY OF PLANTS 



portion of it. Now the nucleus is known to be a distinct organ 

 of the cell, while the protoplasm proper is called the cytoplasm* 

 i.e., the cell plasm. The structure of the cell of spirogyra might 

 be recapitulated as follows: 



Cell wall 

 Chlorophyll band \ 



or 

 Chloroplast 



Sphere of starch grains 



Cell 



Pyrenoid 



Protoplasm 

 in old sense 



Cytoplasm 



Wall layer 



Nuclear layer 



Strands 



Nucleus and nucleolus 

 Vacuoles containing cell sap 



364. The structure of the spirogyra cell represents funda- 

 mentally the structure of all living cells in the resting condition, 

 i.e., when the cell is not dividing. The chlorophyll is absent in 

 many cells, and so are the pyrenoid and starch grains. But the 

 cytoplasm, the vacuoles, the nucleus and nucleolus are present 

 in all living cells. The cytoplasm, nucleus and nucleolus con- 

 stitute the living substance of the cell. By reference to fig. 180 

 of the amoeba, a single-celled animal, these important parts of the 

 cell are seen to be present. 



365. Plasmolysis of the cell.f The plant spirogyra is an 

 excellent one in which to study certain work of the cell. In the 

 normal condition of working cells they are in a condition of 



* Strictly speaking the cytoplasm shows two different conditions or kinds, 

 a very thin outer layer next the wall, which is homogeneous, the ectoplasm, 

 and the inner portion, of a granular nature, the endoplasm. 



j" This subject might well be introduced in connection with the study of 

 methods for strengthening the stem and leaves or in the study of absorption 

 by roots. It is introduced here for the reason that spirogyra is much easier 

 to use than the tissues of the higher plants because no sections are necessary. 

 Also it is convenient in connection with the study of spirogyra as a plant. The 

 paragraph is chiefly for reference. 



