274 MINNESOTA BOTANICAL STUDIES 



A paper by Kellogg (44) contains some general studies of this 

 formation which he terms the "pine type." These observations, 

 which were made outside the sandhills, include the manner of 

 growth, reproduction, rate of growth, and the economic value of 

 the dominant species of this formation which has been very briefly 

 characterized. 



LOWLAND FORMATIONS 



Extensive lowland plant formations are found in many parts 

 of the hills. In general these do not dififer fundamentally from 

 similar groups of vegetation common farther east and all are to 

 be regarded as invasions of typical aquatic, marsh, and meadow 

 species that are not peculiarly characteristic of the sandhills. 



For convenience in this preliminary study all of the lowland 

 plant associations have been grouped under three formations, the 

 water-plant formation, the marsh formation, and the meadow forma- 

 tion. I have included within the water-plant and marsh formations 

 all of the hydrophytes and most of the helophytes of the sandhills. 

 The third formation is composed of species that range from hydro- 

 mesophilous forms to the more mesophytic species of the meadows. 



The Water-Plant Formation 



The water-plant formation occurs in the most pronounced and 

 clearly defined form in the lakes and ponds that characterize certain 

 portions of the region. Such hydrophilous centers are found, as 

 has been indicated in a former subdivision of this study, in east 

 central Cherry County; in southwestern Brown County; in south- 

 western Cherry County, at the headwaters of the Middle Loup 

 River ; in western Hooker County, at the head of the Dismal River ; 

 and in central and northern Garden County. Besides in these major 

 centers the formation is often seen in cut-off ponds along the 

 Dismal and Loup rivers. As a rule, however, the streams of the 

 region are so swift that the water-plants are not often found in any 

 considerable aggregation along their courses except in occasional 

 protected bays. On the other hand many of the lakes and ponds 

 of the region are literally chocked by the members of this formation 

 which occur in extensive tangled colonies. The total volume of the 

 water-plants varies somewhat from season to season. There are 

 rather evident indications of a climatic control which may determine 

 the relative abundance of species for different years. 



