PROTOPHYTES. 85 



of green cells, each surrounded by a gelatinous envel- 

 ope, and sometimes a nucleus, or more solid aggregation, 

 which is considered the center of vital activity, is seen 

 in the cell. The green particles, or granules, which fill 

 the cells, are formed material called chlorophyll. Through- 

 out the vegetable kingdom the presence of chlorophyll 

 is necessary to enable the plant, under the stimulus of 

 bright sunlight, to break up carbonic acid, evolve the 

 oxygen, and appropriate carbon as food. In the absence 

 of sunlight all plants become oxidized, and evolve car- 

 bonic acid. The cells of the Palmogloea multiply by 

 binary subdivision, or fission. (Chap. Ill, Sec. 12.) This 

 multiplication is an act of growth, and differs from simi- 

 lar self-division in the higher plants by the purpose man- 

 ifested, and the plan for a purpose, seen in the " differ- 

 entiation " of cells in the higher orders for the production 

 of special organs. 



In these lowly plants there is a process similar to the 

 plan of reproduction in the more complex forms. A 

 pair of cells will sometimes reunite, or fuse together, first 

 by means of a narrow bridge, and then a larger mass, 

 and finally a complete fusion. The mass is termed a 

 Spore, (from the Greek spora, a seed,) and is the primi- 

 tive cell of a new generation formed by fission. 



3. In a form allied to the above, the Protococcus pluvi- 

 alis, (Fig. 25,) not uncommon in rain-water, a somewhat 

 greater variety of conditions has been seen. It is found 

 still, or quiescent, and motile. In the first form the bio- 

 plasm is surrounded with a wall of cellulose, and filled 

 with granules of green or red chlorophyll. These still 



cells multiply by self-division, each producing two, four, 



8 



