Minnesota Plant Life. 



457 



may be found on the leaves, as on those of the rosemary, the 

 cranberries, and the swamp blueberries. Sometimes the epi- 

 dermis of the leaf or stem is very thick, as in the bulrushes 

 and sedges. Sometimes the leaves are leathery, as in partridge- 

 berries, cranberries and Kalmias, and this is a common adapta- 

 tion among heaths. Sometimes the leaves are small, slender, 

 and with but little surface for evaporation, a character that 

 may be seen in many heaths and sedges. In some varieties the 

 leaves are greatly reduced, as in the scouring-rushes, the bul- 

 rushes, some of the sedges related to the cotton-grasses and 

 many of the true rushes. Or, if present, the leaves may be almost 

 cylindrical, as in the Scheuchzcrias. Again, the leaves may be 

 needle-shaped, as in tamaracks or spruces. If the leaves are 

 broader they often stand vertically so as to expose only their 

 edges to the direct rays of the sun. This is well illustrated by 

 the blue flags, the sweet-flags, the blue-eyed grasses, the yellow- 

 eyed grasses and the cat-tails. Where these broader leaves do 

 not stand vertically they are sometimes rather few in number. 

 This may be seen in the reed-grasses and wild rice. Broad 

 leaves of swamp plants are often rolled in along the mar- 

 gins the same adaptation found among desert grasses. Thus, 

 crowberry leaves and many sedge and grass leaves in the 

 swamp-dwelling species, are rolled. Sometimes the air pores 

 are developed but very poorly on the upper surfaces where the 

 leaves are spread out to the sun. All of these characters may 

 be regarded as limiting the transpiration of the shoot and 

 leaves. 



Special reasons may be given for the leaflessness of some 

 swamp plants, as for the bulrushes which belong to the cate- 

 gory of surf plants. Their leafless, whip-like sterns are adapted 

 to withstand the impact of surf. The temperature, also, of the 

 water has something to do with the appearance of the xerophytic 

 characters. They are more prominent where the water is cold. 

 So especially in peat-bogs and cedar swamps does one find a 

 variety of sedges, heaths, rushes and cone-bearing trees, all 

 characterized by slow evaporation. 



Reed marshes. To the class of reed marshes belong a variety 

 of shore formations and swamp formations common in Min- 

 nesota. Here should be classed the wild rice beds and the beds 



