254 MISSOURI BOTANICAL GARDEN. 



studied, thus explaining the fact that clover docs not ap- 

 pear in acid soils prior to the addition of lime, ashes, or slag/^ 

 Ilicks, in his own experiments, came to the conclusion 

 that unless an excessive amount of lime is apphcd, this 

 substance is helpful to germination. There remains, of 

 course, the question of calciphile and calcifuge plants, but 

 Ililgard,* again calls attention to the fact that while in 



be 



indifferent. 



h 



For these reasons it would seem that in the present instance 



depend 



we may sately ignore the question ot the chemical ( 



of the soil, and that, in this region, under physi 



water is the most important factor in determining tl 



of the vegetation. For though, to a certain extent 



ent on the physical and chemical nature of the soil, in most 



cases it is of greater influence than either and also directly and 



indirectly modifies the temperature of both soil and air. , 



The correctness of this assumption seems to be borne out 

 by the history of the country studied, which, briefly recapit- 

 ulated, is as follows. It formed originally part of an exten- 

 sive peneplain, which, in pre-glacial times, was divided into 

 an eastern and w^estern portion by the trough of the Missis- 

 sippi. After the glacial period the land, at that time at a 

 considerably lower level, wag covered by extensive and slowly 

 moving bodies of water which deposited a fine, almost im- 

 palpable sediment, the loess. As the result of a general 

 uplifting, the loess was exposed and the Mississippi excavated 

 its channel, the position of which has changed in the course 

 of time, shifting towards the Missouri shore. It is not to be 

 supposed that the land, at the time of the uplifting, pre- 

 sented a uniformly level surface. As the bottom of a lake 

 shows areas of greater and less depth, so the plateau prob- 

 ably possessed a more or less uneven surface. Long, gentle 



alternated 



This 



surface was further furrowed by the physiographic forces 

 which continue to exert their influence to the present day. 

 The water of precipitation cut miniature canons in the 

 loess. These, especially where abutting on the bluff, be- 



* Soils, p. 521. See also Science n. s. 37 ; 140. Ja* 24. 1907. 



