PROTOCOCCUS 31 



Sometimes the chlorophyl seems to be scattered all through the 

 protoplasm of Protococcus, but usually it is seen only in a part of the 

 cell ; in the latter case it is located in a body called a chloroplasl, which 

 is a special, rather firm part of the protoplasm. The chlorophyl is 

 used by the plant in manufacturing certain complex foods (especially 

 sugars) out of very simple substances (water and carbon dioxid) which 

 are taken in from the outside. All green plants have this power of 

 building complex foods out of simple ones. Plants that have no 

 chlorophyl, such as the bacteria, cannot do this ; which explains why 

 bacteria must obtain their food ready-made and so are dependent 

 upon other organisms. Each cell of Protococcus also contains a very 

 small nucleus, which cannot be clearly seen except after a special treat- 

 ment of the cell. 



45. Conditions of Life. — In the situations in which it 

 lives, Protococcus must be able to endure dry weather as well 

 as extreme heat and cold. When it has a supply of water, 

 such as may be caught during a rain in the crevices of the 

 bark of a tree on which it lives, it makes sugars and other com- 

 plex foods, as well as new living matter, and grows and 

 divides rapidly. When the water dries up or drains away, 

 the plant ceases to grow, and rests until another supply of 

 water comes to it. It is thought, however, that Protococcus 

 may take in some of the water that it needs from moist air. 

 The carbon dioxid that is necessary is taken from the air; 

 in the water that the cells absorb from the bark or stone or 

 other surface on which they live, there are small amounts 

 of the nitrates and other substances that are needed in build- 

 ing up living matter. 



46. Reproduction. — Like the bacteria, Protococcus re- 

 produces only by a division of the cell, when it has grown 

 to a certain size, into two (Fig. 12, B, C). If the daughter 

 cells separate, each rounds up into a globular form ; but often 

 they remain together, flattened on the sides which touch, 

 thus forming a colony of two cells. By further divisions, 

 colonies of three, four, or sometimes more, cells are produced 

 (Fig. 12, D). The divisions of Protococcus are not all in 

 the same direction, as is the case in the bacillus that we 



