1895.] MICROSCOPICAL JOXJUNAL. 141 



vegetable nature, their classification, and their peculiar 

 spontaneous movements. Their study is now becoming 

 one of practical importance, because it has been found 

 that these little plants are often present in large num- 

 bers in the ponds and reservoirs of our public water sup- 

 plies, and that they cause unpleasant tastes and odors. 



For several years it has been my pleasure to study 

 the diatoms from this practical standpoint. My obser- 

 vations have been confined chiefly to the reservoirs of 

 the Boston Water Supply and to some small ponds in the 

 vicinity of Bostoa, but the published reports of the Mass. 

 State Board of Health have given op23ortunity for com- 

 parison wdth the diatom growths in other localities. 



Of the one hundred and more genera into which the 

 diatoms have been classified there are not more than 

 twenty that are commonly found in our water supplies, 

 and only six have, thus far, been found to be of practical 

 importance, namely, Asterionella, Tabellaria, JMelosira, 

 Synedra, Stephanodiscus and Diatoma. Some of the 

 other genera met with are Cyclotella, Cymbella, Epithe- 

 mia, Fragilaria, Gomphonema, Meridion, Navicula, Nitz- 

 schia, Pleurosigma,Schizonema, Stauroneis and Surirella. 



The six most important genera are not always ob- 

 served in the same reservoir. Usually there are certain 

 diatoms peculiar to certain ponds. Lake Cochituate, for 

 instance, often contains large growths of Asterionella, 

 Tabellaria, and Melosira, and smaller growths of Syned- 

 ra and Stephanodiscus. Basin No. 3 contains Asterio- 

 nella, Tabellaria, Synedra, but no Stephanodiscus nor 

 Melosira. In Basin No. 2 only Synedra and Cyclotella 

 are found. Fresh Pond, Cambridge, is famous for its 

 Stephanodiscus, and Diatoma is often very abundant in 

 the Lynn waters. Furthermore, there are ponds where 

 diatoms are never found, except in very small numbers 

 at rare intervals, while in neighboring ponds they may 



