8 Minnesota Plant Life. 



dominated by grasses with prostrate underground stems woven 

 together into a solid and matted turf, thrusting into the air only 

 their side-branches and thus giving to the whole a flat and level 

 character. It is not very well known precisely why the prairie 

 type of vegetation has established itself over such large areas of 

 the world. Some have attributed it to fires, others have thought 

 that climate and soil are responsible for the difference between 

 prairie and forest. Perhaps all that need be said is that there 

 are these two principal methods of developing plant-stems. 

 When the dominant plants of an area are such as have acquired 

 the habit of trying to avoid each other's shade by elongation of 

 their stems, that region is a forest. When, on the other hand, 

 an area is occupied by plants that have learned to elbow each 

 other beneath the surface of the soil, that region is a prairie. 

 It is a mistake to suppose that the lofty tree is in every sense 

 stronger than the modest grass, for the two have simply devised 

 different means of accomplishing the same result. A prime 

 necessity of most plants is sunlight, since without it they are 

 unable to construct their food from the gases of the atmosphere 

 and the water of their sap. Therefore, they must have light, 

 and to obtain it they adopt instinctively the methods of growth 

 which will enable them to do their own life-work regardless of 

 their neighbors. The pine tree may be described as a plant 

 which for ages has been solving the problem of better illumina- 

 tion by a progressive increase in height. The grass, by copious 

 ramification of a protected underground stem upon which lat- 

 eral leaf-bearing branches are produced, in its way strives to 

 obtain illumination, nutriment and persistence. 



Another difference which exists between the forest and prairie 

 of Minnesota is in the direction from which the plants have 

 come. The forest is, in large part, composed, so far as its domi- 

 nant plants are concerned, of northern forms, while the prairie 

 is inhabited rather by immigrants from the south. So on a 

 map illustrating plant distribution in the northern hemisphere 

 it will be found that the prairies in Europe, in Asia and in 

 America lie south of a forest belt. It is true that in the tropics 

 around the world a forest region exists, broken only by deserts 

 like those of the Sahara, or northern Australia ; but in regions 

 beyond the tropics it would seem that in both hemispheres there 



