66 CELL INTELLIGENCE THE CAUSE OF EVOLUTION 



roots, stems and leaves, although they may contain mil- 

 lions of cells 



"Bounding the cell there is a thin elastic cell-wall com- 

 posed of a substance called cellulose. The cell-wall, 

 therefore, constitutes a delicate sac, which contains the 

 living substance. It is the substance that has formed 

 the wall about itself in the same sense that a snail deposits 

 the shell about its body. It is organized into various 

 structures which are called organs of the cell. One of 

 the most conspicuous organs is the nucleus, a compara- 

 tively compact and usually a spherical body and gener- 

 ally centrally placed within the cell. 



"The fungi do not contain chlorophyll and this fact 

 forms the sharpest contrast between them and the algae. 

 The presence of the chlorophyll enables the algae to be 

 independent of any other organism since they can manu- 

 facture their food out of carbon-dioxide and water. The 

 absence of chlorophyll compels the fungi to be depen- 

 dent upon other organisms for their food. This food is 

 obtained in two general ways: either (1) directly from 

 living plants and animals, or (2) from organic waste 

 products or dead bodies. In case a living body is at- 

 tacked, the attacking fungus is called a parasite and the 

 plant or animal attacked, the host. In case the food is 

 obtained in the other way, the fungus is called a sapro- 

 phyte. For example the rust that attacks wheat is a 

 parasite and the wheat is the host ; while the mold which 

 often develops on stale bread is a saprophyte. 



"Bacteria include the smallest known living forms. 

 Even to distinguish ordinary bacteria, the highest powers 

 of the microscope are necessary and to study them is too 

 difficult for the untrained student. However, they are so 

 very important to man on account of their useful and 

 destructive operations that every student should have 



