Minnesota Plant Life. 451 



at all abundant in the greater number and most of the stems 

 and leaves are limp when taken from the water. In the cortex 

 of the stems and leaf-stocks air chambers are common. 



A variety of propagative processes are characteristic of water 

 plants. Sometimes they pass the winter in an evergreen state 

 at the bottom of ponds under the ice. The eel-grasses and 

 water starworts do this. Sometimes their leaves are destroyed 

 by the winter's cold and new ones are produced from storage 

 areas of the rootstock, from buds, or from special propagative 

 bodies. The special propagative bodies of water plants are 

 very interesting. The pondweeds sometimes form little buds, 

 that are separated from the plant body and become distributed 

 to a distance. The bladderworts are remarkable for their pro- 

 duction of green winter buds, known as hibernacida, which, in 

 the autumn of the year, or in the spring, may be seen at the 

 end of bladderwort stems. In such buds the leaves are very 

 densely crowded together into a diminutive green cone and 

 the sections of the stem with crowded leaves may be sepa- 

 rated from the general plant body and serve to propagate the 

 species. The calla, rather a marsh than a water plant, but 

 often living in the water, has a similar habit of separating win- 

 ter buds as propagative organs. 



The distribution of different kinds of shore and bar plants 

 depends upon a variety of conditions, the character of the soil, 

 the depth of the water, its quiet or agitation, and its tempera- 

 ture. The bass-\veeds form the deep water zone. Warming 

 states that they may grow in 75 feet of water, but usually 

 they do not grow nearly as deep as this. The waterweeds pre- 

 fer shallower water, the pondweeds still shallower, while the 

 water-lilies grow close to the reed-grasses and bulrushes. The 

 latter are accounted also as marsh vegetation, because so much 

 of their starch-making surface is lifted above the water. 



The reproductive processes of water plants of this group 

 retain the characters of the original land habitat, so far at least 

 as the flowering plants are concerned. Thus, the flower clus- 

 ters are always produced above the surface of the water, and 

 pollination is effected either by the wind, by currents of water, 

 by wind and water combined, or by insects. Where the flowers 

 are conspicuous, as is true of water-lilies or pond-lilies, insect 



