THE SINGLE CELL 199 



2. Most plants are thus composed of numerous Cells. But 

 many of the lower classes (e. g., Bacteria) consist of a single cell 

 each. These plants are generally very small. 



3. The Size and Shape of the cells vary greatly. In the 

 Bacteria the length of one is less than -001 cm, in the fibre of 

 Flax and the hair of the Cotton-seed it extends over 4 cm. Their 

 shape may be spherical (as in the pollen grains), or cubical, or 

 brick-shaped (many epidermis cells) or cylindric, or tapering 

 towards both ends like a torpedo (as the bast cells of most plants). 



4. In some cases a number of cells standing one over the 

 other in a row have the partitions which separate them removed, 

 and thus form a tube or a Vessel, open all through. 



Plants, then, are built up of cells, or of cells and vessels, the 

 latter originating from cells. 



5. The cell consists of a cell-wall and the cell-contents, 

 which when young is called Protoplasm. This is a viscid, nitro- 

 genous substance, capable of absorbing moisture, of expanding, 

 of forming fresh cells by division, and of motion: it is endowed 

 with life. The cells are the workshops in which all the secret 

 and wonderful operations of the plant-life are carried on. 



6. By the activity of the protoplasm certain substances are 

 produced, which are of great importance to the life of the plant. 

 Some of these are green granules, called Chlorophyll, which give 

 the plants their green hue. The chlorophyll-granules have the 

 power of forming starch under the action of sunlight out of car- 

 bonic acid gas and ^vater absorbed by the plant. 



7. Besides, the cells contain a fluid, called the Cell-Sap, in 

 which sugar, acids (citron), salt, and other substances are dis- 

 solved. This sap rises from cell to cell, permeating through the 

 cell-walls from the root to the top of the tree. The protoplasm 

 forms various substances out of the cell-sap, which are either 

 passed along to any point of activity where their presence is 

 necessary for the growth of the plant; or they are stored up in 

 the tissues of the plant for future use. In this way starch, oily 

 and fatty matters, and grains of protein are formed and stored. 



