March, 1921] Macro-Fauna of Mirror Lake 145 



PART IV. 



ECOLOGY OF MIRROR LAKE. 



A. The Flora of Mirror Lake. 



It is only as an environmental factor that plants are con- 

 sidered in this survey. As with the fauna, the microscopic flora 

 was not collected or observed. 



The large pond was practically free of larger algae as well as 

 of higher plants, except for some favorable littoral situations. 



Covering all of the upper surfaces of submerged rocks (as 

 noted along most of the north shore) were good growths of 

 filamentous algcC, including Spirogyra of several species, and 

 Cladophora fontanemus, (rocks at station 4), Spirogyra fliiviatilis, 

 and Oedogonium, (rocks at station 7). Cladophora and 

 Oedogonium were found on rocks at station 6. In the shallow 

 waters of station 9, both on small stones at bottom and forming 

 masses drifted in towards shallowest part were various species 

 of Spirogyra. Directly north of the wooden bridge were 

 Mougeotia sphccrocarpus and Spirogyra of various species 

 including 5. eaten if ormis. 



In the small pond a great development of plants took place 

 each summer. Extensive growths of Spirogyra, Cladophora, 

 Vaucheria, and Oscillatoria limosa, were found in this water. 

 A complete list is not available as material for determination 

 was collected only once, rather late in summer. 



The dtickweed, Lenina minor, beginning in small isolated 

 groups of leaflets in spring, multiplied rapidly and by late 

 summer formed a dense mass like a green carpet covering the 

 water. The duckweed seemed to obliterate the algae to a 

 marked extent. Only along station 3 was there an area free 

 from it. There were practically no other higher aquatic 

 plants present. 



Along the shore of the small pond grasses grew luxuriantly, 

 and by fall these encroached upon the water. The chief grasses 

 were Dactylis glomeratiis (orchard grass), and Leersia oryzoides 

 (saw grass or rice cut grass). Small patches of these were found 

 in very shallow water just off shore, in the southern end of 

 the small pond, at station 12, and likewise north of station 9 

 and of the rustic bridge in the large pond. Bur marigold, 

 Bidens connata mingled with grasses along shore especially where 

 much moisture prevailed. 



