knowledge gap in the belief that some awareness of the river's native 

 flora, if heeded, will be beneficial for guiding future management 

 of the river. The Yellowstone remains, following this brief overview 

 and what has been accomplished before, an ecological frontier for serious 

 research in phycology. 



A five-part series on the microflora of the Yellowstone River is 

 proposed. Parts I and II preceded this report. Part I (1) reported 

 on three phytoplankton samples taken near the confluence of the Bighorn 

 River early in 1973. The non-diatom algae from those samples are in- 

 cluded in the report, along with the correction of a taxonomic error 

 committed in Part I. Part II (3) took an intensive look at the micro- 

 flora of the middle river between Laurel and Huntley and described its 

 response, in terms of indicator species and species diversity, to a 

 variety of discharges entering the river in that stretch. 



Parts IV and V will follow this report. Part IV will deal with 

 the diatoms, unquestionably the most diverse and perhaps functionally 

 the most important group of algae in the river. It is estimated that 

 between 300 and 400 species and varieties of diatoms inhabit the Yellow- 

 stone. Because diatoms are the author's specialty and area of primary 

 interest, and because of their apparent importance in the river's trophic 

 structure, the major share of his effort will be spent on Part IV. The 

 final installment. Part V, will attempt to predict the effects of altered 

 flow regimes, including impoundment and dewatering, upon the composition 

 of the river's algal associations and their ecologic and economic 

 implications. 



