278 The Plant World. 



The rainfall, which averages about 32 inches, is fairly evenly 

 distributed throughout the year, but there are sometimes periods 

 of several years in succession when the precipitation is less than 

 the average by several inches. This condition of affairs, together 

 with the fact that in the county are numerous sandy areas the 

 soil of which quickly dties out, has resulted in a conspicuous 

 representation of xerophytic types. 



It is a matter of much interest connected with the study of 

 local distribution that the different soils in the county, which are 

 of many types, from coarse bouldery gravel to fine clay, and from 

 dry, barren sands, through rich, black loam to wet clay and pure 

 organic materials, are arranged in a series of long narrow strips, 

 often very sharply defined, on which there is a zonal arrangeinent 

 of plants corresponding to these types of soil and to the ground 

 water level determined by the physiographic development of 

 the area studied. The resulting variety of conditions is reflected 

 in a great variety and heavy growth of native vegetation. The 

 whole region before its settlement was heavily timbered. A 

 dense forest of elm, black ash, soft maple, .sycamore, swamp oak, 

 white ash, basswood, and other water-tolerant trees which oc- 

 cupied the heavy, undrained, or poorly drained, clay soils near 

 the bay and extended to some distance inland. Penetrating 

 this forest on the ridges, where the drainage was good, was the 

 beech and maple forest, the beech often dominant, or associated 

 with elms, bur and red oaks, or, on the drier areas, with hard 

 maples. In this mesophytic forest white and black oak often 

 appeared, and still more frequently the white pine, which be- 

 came dominant where the sandy elements of the soil were in 

 excess; and in some instances, as in the Cass valley, a pure white 

 pine forest — practically a xerophytic coniferous forest — oc- 

 cupied considerable areas. The s\wamp coniferous type of forest 

 was represented by relatively restricted areas of tamarack, 

 arbor vits, and black spruce, in wet swamps and along the mar- 

 gins of small lakes. Finally ,a remaining type, the xerophytic, 

 broad-leaved forest, in which oaks were dominant, was sparingly 

 represented on certain areas, where, however, it appears neverto 

 have been able to maintain itself to any great extent in compe- 

 tition with the white pine. 



