462 Minnesota Plant Life. 



Inlet, dry peat-moss turfs form in the dej^ressions of the rock. 

 Mingled with the peat-moss were the reindeer-moss lichens 

 and the hluehells and juniper 1)ushes, which are such distinctive 

 rock plants of this region. 



Swamp underbrusii. Another type of swamp vegetation de- 

 veloped in Minnesota is known as swamp shrub or swamp 

 underbrush. This consists for the most part of birches, wil- 

 lows, buckthorns, black haws, hollies, dogwoods, alders and 

 poison sumacs. Where a reed swamp or wet meadow has 

 grown up to underbrush this sort of formation appears. When 

 the swamp underbrush has arisen, sufficient shade is produced 

 to permit the development of certain accessory herbs that 

 w^ould not otherwise be so abundantly present. In such re- 

 gions, for example, violets and touch-me-nots, gentians and 

 thoroughworts are often abundant. Such swamp underbrush 

 sometimes grows along the edges of peat-l)ogs and lakes and in 

 this situation willows and dogwoods particularly abound. Wil- 

 lows, also, very often form rings around the shores of small, low 

 islands, mud flats, or sand bars in lakes or streams, while the 

 higher land of the centre is occupied by elms, cottonwotxls, 

 maples or basswoods. This is a very common example of 

 zonal distribution in Minnesota. 



There have now been passed in review the principal types 

 of hydrophytic vegetation. Apparently the strong preponder- 

 ance of water in the substratum, as for the swamp plants, or 

 surrounding the plant body, as for aquatic vegetation, has a 

 number of definite inlluences not only upon the structure of 

 plants, but upon their grouping. The depth of the water, the 

 character of the soil, the chemical substances held in solution 

 in the water, the temperature, agitation, or quiet, and other 

 conditions, all have their influence and it is not at all an acci- 

 dental matter whether a particular moist region develops as a 

 peat-bog, as a reed swamp, as a wet meadow, or as a swampy 

 underbrush. in all the hydrophytic vegetation classes peren- 

 nial species are predominant. .\ great many of them are 

 herbs, while some are shrubs, and a few are dwarfed or spe- 

 cialized trees. 



