PLANKTON IN WATER SUPPLY — MEIER 395 



had recorded serious trouble due to vegetation in their reservoirs. 

 Since that time, thousands have recorded similar difficulties. To the 

 Massachusetts State Board of Health belongs the credit for having 

 begun as early as 18S7 a systematic examination of all the water 

 supplies in that State. 



THE PLANKTON 



The uninvited guests which cause so much difficulty in our water 

 supplies are classed under the term plankton. In 1887 Hensen, of 

 Germany, jjublished a new method for studying the minute floating 

 organisms found in lakes. He gave these organisms the name "plank- 

 ton" from the Greelc word "planktos," which means "wandering." 

 Plankton includes the free-floating or weakly swimming organisms, 

 algae and bacteria (minute plants), and protozoa (minute animals) 

 that form an independent group in a body of water. Plankton rarely 

 causes disease nor does it often spread organisms that do. The pres- 

 ence of plankton is generally made known in the water supply by the 

 appearance, taste, or odor of the water and interference with the 

 operation of the filter plant. 



ALGAE 



Algae (pis. 4, 5, 6) make up the largest number of the plankton in 

 the water supply. They represent one of the lowest divisions of plant 

 life and are characterized by the absence of roots, stems, leaves, 

 flowers, and seeds. Some species are composed of single cells, which 

 are microscopic in size; others consist of clumps of cells; and still 

 others consist of numerous cells bound together in long threads or 

 filaments, which are able to attach themselves to submerged objects. 

 We are all familiar with algae that form the green scum of ditches 

 and fish ponds and make a green coating on old stone walls and trees. 



Algae have differences in pigment that serve as a basis for their 

 classification although they all contain the green pigment, chlorophyll, 

 even when it may be screened from view by another pigment. The 

 Chloro'phycecie are the true green algae, the Cyanophyceae are the 

 blue-green, the Phaeophyceae are the brown, and the Rhodophyceae^ 

 the red algae. The two latter classes of algae consist mainly of the 

 marine forms, therefore the ChJ'Orop'hyceaje and the Cyanophyceae are 

 the two classes of algae occurring most frequently in our water sup- 

 plies. The diatoms (pi. 3) often associated with the algae have a 

 yellow pigment and a siliceous shell constructed like a pill box. 



One important characteristic of the algae from the point of 

 view of the waterworks engineer is their power of rapid multiplica- 

 tion, which enables great numbers to appear in a very short time 

 provided environmental conditions are favorable. Their simplest 



