Minnesota Plant Life. 445 



Salvinia plants is taken between the thumb and finger and 

 thrust under the surface of the water, air is imprisoned between 

 the tufted hairs and the whole plant glistens as it is submerged. 

 If it is released it rises instantly to the surface, buoyed up by 

 the air chambers in its leaves and stem, and when it emerges 

 the upper sides of the leaves will be found perfectly dry. 



Of the planktonic flowering plants of Minnesota, some de- 

 pend upon the wind for pollination, as do the duckweeds, while 

 others, such as the bladderw^orts, are adapted to insect pollina- 

 tion. The flowers, therefore, of the duckweeds are extremely 

 inconspicuous, while those of the bladderworts are pretty, yellow, 

 snapdragon-like and elevated upon stems some inches in length, 

 so that they become noticeable objects and are easily found 

 by wandering bees or flies. Some free-floating or plankton 

 plants are particularly protected against the attacks of small 

 aquatic grazing insects or animals, while the bladderwort actually 

 catches and eats the little insects that gather in its vicinity. 

 The Salvinia plant is provided, on its submerged counterpoise 

 leaves, with sharp-pointed hairs, and these stand out on every 

 side in bristling defence. The sharp-pointed hairs are par- 

 ticularly useful because the fruits of the Salvinia are borne 

 under water, on the submerged leaves, and it is important that 

 they should be protected. The under sides of the floating 

 leaves have also a defence of sharp-pointed hairs, but the hairs 

 on the upper side, since they have a different purpose — that of 

 keeping the surface dry — are of different structure. 



Swimming plants. Closely related to the plankton, or free 

 floating vegetation, are the animal-like little plants that swim 

 about in the water seeking decaying organic substances upon 

 which to feed. They are abundant in stagnant water where 

 there is sufficient organic food material. A Minnesota plant, 

 known to botanists by the name of Euglena, is an example of 

 this class of hydrophytes. It is able, by means of its green color, 

 to assimilate carbonic-acid gas in the presence of sunlight. It 

 takes up its nitrogenous food from the organic substances dis- 

 solved in the stagnant water and is, therefore, in its method of 

 nutrition, partially dependent. The Euglena plants are of 

 microscopic size and countless myriads of them in stagnant 

 pools often form dense green scums of a granular appearance. 

 Zoologists consider them animals. 



