Minnesota Plant Life. 



447 



the contrary, air chambers are often entirely absent. Where, 

 too, the plant is anchored and free to undulate its branches 

 with every ripple of the water there is little occasion for strong 

 mechanical tissues, and no need for air pores or any of the 

 devices for protecting- them. Elastic tissue is, however, some- 

 what useful, and in many plants of this class it is formed. A 

 great number of the submerged plants are slimy to the touch, 

 especially in the ocean. This is well known to be true of sea- 

 weeds and it is also the case with river moss and riverweeds. 

 Such slime-coverings may be useful as protections during 

 periods of low water, or they may reduce the friction, upon the 



tissues of the plant, of the 

 flowing water. 



Still another class of water 

 plants are attached under 

 water to loose soils, sand or 

 mud. The water eel-grasses 

 may, perhaps, be taken as 

 examples of this group. 

 Holdfasts are not here de- 

 veloped simply as anchors, 

 but there may also be 

 branching root systems 

 upon which, however, root 

 hairs are often wanting. 



Shore and bar plants. 

 The most important class of 

 water plants that are of 

 genuine aquatic habit, so 

 far as developed in Minne- 

 sota, are those which may 

 be known as the shore 

 plants and bar plants. These are attached or submerged vari- 

 eties, growing upon loose soil, generally in communities, with 

 the plant body either entirely submerged or with the leaves 

 floating. The flowers are entirely aerial and pollination cannot 

 go on under the water. It is difficult to distinguish this class of 

 aquatic plants from the related swamp plants that grow close 

 down to the water's edge; and in fact, sometimes the same 



FIG. 220. Vegetation of ravine. The home of 

 mosses and liverworts. The plants in 

 front are touch-me-nots. After photograph 

 by Williams. 



