446 Minnesota Plant Life. 



Rain-water plants. A little class of obscure plants are re- 

 garded as of hydrophytic character, since they live on rain- 

 water. The green slime that forms upon mud flats, the 

 bacterial skins that arise upon soil highly charged with or- 

 ganic substances, the blue-green algae that thrive between the 

 particles of sand upon a moist beach, and the curious algal or 

 bacterial organisms that live under the surface of damp sand- 

 stone cliffs, looking like cobweb threads when a bit of the cliff 

 is chipped off, might be given as examples of this class. 



Attached water plants. Another adaptational class of hydro- 

 phytes is furnished by those species which live attached to 

 stones, either at the bottom of streams or lakes, or upon the 

 surfaces of wet cliffs, or those of bowlders exposed to spray. 

 Several algae are found in such localities. On \vet cliffs a variety 

 of green algae are to be looked for, and here, too, especially 

 near waterfalls, will be found the very few kinds of red algae 

 which occur in Minnesota. Sometimes a dark brownish-purple 

 skin of slimy algae may be seen on cliffs wet by the spray of 

 waterfalls, and this may be a growth of red algae. In similar 

 localities, and on stones in rapidly running streams, the wire 

 like, reddish-brown algae of the Minnesota flora are to be 

 sought. 



Some higher plants select similar localities for example, the 

 river moss so common in swift, rock-bottomed streams, where 

 it grows attached to stones and lies in tufts with the cur- 

 rent. The very curious riverweed, of which one variety exists 

 in Minnesota, affixes itself to stones in waterfalls, and closely re- 

 sembles an alga. It is remarkable because it is the only kind 

 of Minnesota flowering plant that opens and pollinates its 

 flowers entirely below the surface of the water. A character- 

 istic structure of attached rock plants in rapid water is the 

 holdfast, an organ which has more the office of an anchor than 

 of an ordinary root. In the river moss the ordinary slender 

 root hairs characteristic of mosses are gathered together in 

 strands, thus giving additional strength, and by means of these 

 little cables entwined around the rough corners of the stones 

 the plant holds itself in place. Plants of this sort with hold- 

 fasts and with submerged vegetative tracts naturally do not 

 have abundant air chambers as in the floating 1 varieties. On 



