28 DARK-GREEN SCUM. 



Pleurococcus, Nostoc, and Oscillatoria represent forms 

 of simple plant life. For convenience of study Pleurococ- 

 cus has been placed first ; but in its more highly organized 

 nuclei and chlorophyll bodies, and in its modes of repro- 

 duction, it shows a somewhat higher order of develop- 

 ment than Nostoc and Oscillatoria. The latter, how- 

 ever, in the arrangement of its cells offers an excellent 

 introduction to the higher filamentous forms, to be 

 taken up next. 1 



1 If there is abundant time, it will be found advantageous at this 

 point to take up a study of other representatives of the Cyanophyceae 

 and unicellular Chlorophycese. Several genera of Cyanophyceae are 

 suggested in connection with the "Preliminary" of Nostoc study, p. 21. 



