1002 MINNESOTA BOTANICAL STUDIES. 



humus or drift, but frequently also in crevices submerged be- 

 low the surface. Floating- vegetation, such as Lemna or Riccia, 

 does not form part of the surf-bar>riers, nor do plants with 

 large leaves offering resistance to the waves, such as Castalia, 

 Nymphaea or Poiamogeton natans, although even these can 

 maintain themselves in pretty rough water. Again vegetation 

 with large floating areas and slender attachments to the soil, 

 which may even ordinarily become disconnected, as in the 

 Lentibulariaceae, do not form surf- barriers, for they are too 

 easily uprooted and carried on the shore. The conditions of 

 vegetation, then, result in the selection of a few species of pe- 

 culiar type for this special habitat. 



At Lake of the Woods, five genera of plants seem able to 

 maintain themselves in regions exposed to long continued or 

 intermittent surf. These are Scirpus, Phragmites, Polygonum, 

 Spiraea, and Salix. Surf-barriers, also of Equisetum limosum 

 doubtless exist in the region, having been observed in the 

 Rainy lake country and in central northern Minnesota. None 

 were seen at Lake of the Woods. Of these surf- barrier plants 

 some seem able to withstand strong and long continued surf 

 while others select less exposed shores and are to be looked 

 for rather on the windward side of islands or points and in 

 coves and bays. Hence the classification that has been pro- 

 posed seem justifiable and the five types may be discussed 

 briefly in their order. 



Barriers in strong surf. Of these I find only two types as 

 follows: 



I. Scirpus barrier. The formation is composed of plants of 

 Scirpus lacustris rooted in drift or humus soil and may exist in 

 regions as exposed to surf as any that can afford a foothold for 

 higher plants. Parenthetically, it may be noticed that lichen - 

 formations on surf-washed ledges cannot be regarded as surf- 

 barriers, although certainly they are a type of cumaphytic 

 vegetation. The peculiar structure of Scirpus makes it a surf- 

 plant par excellence, and it is of cosmopolitan distribution in its 

 favorite habitat. Yet at Lake of the Woods it is by no means 

 so abundant as another plant of quite different appearance, by 

 no means so perfectly adapted, yet occupying many exposed 

 shores together with or to the exclusion of the bulrushes. This 

 is the type of a second form of barrier in strong surf. 



II. Polygonum barrier. The species thus established is 

 Polygonum emersum, and especially off rocky points or islands 

 it seems to flourish. Unlike Scirpus which appears to need 



