1894. 



MICROSCOPICAL JOURNAL 



379 



The eye will readily divide the side of a small square 

 into fifths, and this division will be the side of the stan- 

 dard unit square. Thus the size of the unit may be kept 

 constantly before the eye of the observer. 



Table tchich will he found useful in estimating the number of standard units in 

 jUamentous algse. 



Diameter of Filament Number of Standard Units for* 



each hundred microns of length. 

 No. 1 0-5 0.8 



2.0 



4.0 



6.0 



8.5 



11.0 



13.5 



16.0 



18.0 



20 



List showing the ordinary value, in standard units, of some of the organisms 

 found in the Boston Water Supply. 



DIATOMACE^. 



Asterionella. 0.4 Navicula. 0.2 to 1.0 



Cyclotella. 0.1 to 1.0 Stephanodiscus. 1.0 



Diatoma. 0.3 Synedra. 0.2 to 2.5 



Fragilaria. 0.8 Tabellaria. 0.9 



Melosira. 0.5 



Closterium. 



Staurastrum. 



Cosmarium. 



Coelastrum. 

 Gonium. 

 Pandorina. 

 Pediastrnm. 



Anabaena. 



Chroococcus 



Clathrocystis. 



Crenothrix. 



DESMIDIE^. 



0.8 to 6.0 Xanthidium. 

 1.8 Micrasterias. 



3.8 



CHLOROPHYCE^. 



4 . Protococcus. 

 2.0 Eaphidium. 

 7.0 Scenedesmus. 

 5.0 

 CYANOPHYCE^. 



2.0 to 5.0 Ck)elosphaerium. 

 1.3 Microcystis. 

 10.0 to 100.0 



FUNGI. 



2. Beggiatoa. 



3.0 

 6.0 



1.2 



0.8 

 0.3 



5.0 to 50.0 

 2.0 to 10.0 



2.0 



I'The smallest squares of the micrometer are one hundred microns on a side. 



