﻿48 BOTANICAL GAZETTE [January 



From the present study it appears that the most important 

 soil factor in the distribution of the flora of Kent county is this 

 one of the relative ability of the superficial layers to retain water. 

 In other words, the controlling soil condition is one of drainage. 



Throughout the southern half of the county, soils which 

 retain much water are covered with society I, II, or III. The 

 only exception to this is the small clay area within the bend of 

 Grand River. The soil of this area is apparently as good as that 

 farther south, but it is very dry in dry weather, and there is no 

 marked humus covering. Perhaps the proximity to the well 

 drained valley on either hand has an influence through under- 

 ground drainage, but this was not looked into, and the question 

 must be left for the present unanswered. 



Within the sand plain area of the southern half of the county 

 there are several small stretches of societies I and II. Owing to 

 the fact that at one time a much larger stream than the present 

 one flowed through the valley of the Thornapple River, that valley 

 has a well marked terrace between the country level and the 

 present flood plain. This old flood plain is sandy and corres- 

 ponds in manner of formation to the Grand Rapids sand plain. 

 But in very many places this terrace is covered with societies I 

 or II. Some of the finest "sugar bushes" to be seen in the 

 county are here. The sandy soil is thickly covered with a layer 

 of humus. These strips of hardwood are so narrow that they 

 could not well be shown upon the map The same condition 

 holds on the rather high part of the plain lying west of Crosby. 

 This is indicated upon the map. Also at the base of the escarp- 

 ment forming the margin of the deeper glacial channel in the 

 Grand Rapids sand plain, there are several instances of societies 

 I and II upon humus-covered sand. Notably is this true near 

 the southwest corner of Grand Rapids and on the margin of the 

 Buck Creek valley near the Lake Shore and Michigan Southern 

 railroad. In this connection it is interesting to note that beech 

 trees are found quite commonly upon the humus-covered estab- 

 lished dunes along the east shore of Lake Michigan.^ 



5 Dr. Cowles tells me that he has seen these beech covered dunes as far north as 

 Frankfort, and Mr. Whitford has observed them on Manitou Island. 



