384 Minnesota Plant Life. 



Bladderworts. Relatives of the figworts are certain very 

 extraordinary aquatic plants known as bladderworts. In Min- 

 nesota all the forms live in the water, except a little plant called 

 the butterwort, which grows upon rocks along the north shore 

 of Lake Superior. In the tropics, however, a number of blad- 

 derworts grow as perching plants upon tree trunks. For the 

 most part, true bladderworts have no roots, but extend in the 

 water their much-branched, floating body, from which slender 

 stalks arise, bearing yellow, snapdragon-shaped flowers. The 

 leaves of these plants are decidedly compound and consist of 

 thread-like divisions, upon which are produced, usually in large 

 numbers, little, clear, flattened, shrimp-shaped bladders. Each 

 bladder contains generally a bubble of gas along with some 

 liquid, and by aid of the bubbles the plants are enabled to float 

 free in the water. Being surrounded by liquid, they have little 

 need of roots, and have therefore abandoned them. The blad- 

 ders are not, however, employed solely as floats, but each one 

 has an aperture, guarded by a trapdoor, which opens inward 

 but not outward. Small aquatic insects find their way into 

 these bladders, but cannot escape, since the door of the bladder 

 cannot be opened from within. Digestive glands are present 

 on the inner surface of the bladders, and the bodies of the little 

 animals are used by the plant as part of its nutriment. Blad- 

 derwort stems resemble somewhat those of the water-milfoils, 

 but the latter are not free floating plants and are attached to 

 the bottom, nor have they the remarkable shrimp-shaped blad- 

 ders on their leaves. Bladderworts in flower are immediately 

 recognized, for no other free-swimming plants produce two- 

 lipped flowers. Each corolla is provided with a spur like that 

 of the toad-flax flower and is visited by insects which effect 

 pollination. The fruiting capsule is like that of the figworts, 

 with numerous small seeds. In Minnesota there occur five va- 

 rieties of bladderworts to be discriminated by minute differ- 

 ences in the flowers, leaves and bladders. 



Butterworts. A close cousin to the bladderworts is a curi- 

 ous little plant known as the butterwort. It grows in the 

 crevices of rocks along the north shore of Lake Superior, reach- 

 ing in such stations a height of three or four inches. The 

 leaves are oblong, clustered at the base of an erect axis that 



