Minnesota Plant Life. 453 



The depth at which ((iioiulani kind plants are alMe to grow is 

 in some instances very great. Thns Magnin is authority lor the 

 statement tliat one variety of moss was found at a depth of 

 nearlv 200 feet in an Alpine lake, showing on the part of an 

 originally terrestrial plant a very high degree of adaptation to 

 the acjuatic life. Nothing of this sort is known to occur in 

 Minnesota, and l)eyond 25 feet only algce and bacteria are 

 likelv to be disco\ered, while into such deep water pondweeds 

 and waterweeds rarely extend. 



Abyssal vegetation and modified hydrophytes. The vari- 

 ous classes of hvdrophytes which have been discussed may be 

 grouped under the general name of aquatic vegetation. Some 

 forms of aquatic \egetation are scarcely represented in Minne- 

 sota, — for example, hot spring vegetation, the various seaweed 

 classes, and snow^ vegetation. Those which have been discussed 

 comprise the bulk of Minnesota aquatic species. The class de- 

 scribed by Warming as abyssal vegetation occurs, however, in 

 the deep waters of Minnesota lakes from 50 feet below the 

 surface to greater depth. The darkness is so great in such 

 abysses that green plants scarcely exist, though blue-green algae 

 and diatoms are known to occur at depths from 250 to 300 

 feet, being able to utilize the extremely small amount of light 

 wdiich penetrates to them. ]\Iost abyssal forms are bacteria. 

 These occur in the deepest waters, either suspended or in lilms 

 along the bottom, forming, in such depths, a li\-ing slime or ooze, 

 as may be determined by microscopic examination of deep lake 

 soundings. The bacterial vegetation occurs also in moist or- 

 ganic substrata, such as the bodies of animals, where a large 

 percentage of the substance is water. So the parasitic bacteria 

 of disease, either of plants or of animals, might possibly be 

 descril)ed as forms of hydrophytic vegetation. The bacteria, 

 too, which live upon decaying organic matter, such as the sul- 

 phur l)acteria and the ferment-producing bacteria, may be re- 

 garded as constituting a sort of water-loving vegetation, and, 

 therefore, may be classified here. 



Swamp vegetation. The remainder of the hydrophytic 

 classes may be included under the general term of swamp 

 vegetation. This is the plant group that shows itself typic- 

 ally in swamps, in bogs, in marshes, moors and tundras. 



