CHAPTER XXXVI 



THE CELL 



436. Plants Composed of Cells. — All the higher plants 

 arc made up of a large number of small structures termed 

 cells. They are so minute that, in most cases, they are 

 invisible to the naked eye. These cells are box-like structures. 

 They are of many forms. Many of the lower forms of plants, 

 as bacteria, yeasts, spores of fungi, and many of the algae, 

 are composed of but a single cell. 



437. Cells are of Many Forms. — In general, plant cells 

 may be assigned to some one of the following forms: 



Spherical, as in protococcus (a minute alga to be found 

 on damp walls and rocks), and apple flesh; 



polyhedral, or many-sided, as in pith of elder; 



tabular, or flat, as in epidermis of leaves; 



cylindrical, as in vaucheria, spirogyra (fresh water algae) ; 



fibrous, as cotton fibers; 



vascular, as the ducts of wood; 



stellate, as in the interior of leaves of lathyrus (sweet 

 pea) and other plants. 



438. Parts of a Cell. — The typical cell is composed of 

 living and dead matter. The living matter of the cell is the 

 protoplasm. The protoplasm is differentiated into a nucleus, 

 cytoplasm and plastids. 



439. The nucleus is usually a round or elliptical body, 

 denser than the remainder of the protoplasm, in which it may 

 be imbedded or from which it may be suspended by strands 

 of protoplasm called cytoplasm. The cytoplasm lines the wall 

 of every living cell, and commonly in old cells the nucleus 

 is in this layer of cytoplasm. In the cell may be aggregates 



(263) 



