IOWA ACADEMY OF SCIENCES. 175 



Plants cannot anchor themselves because the soil is sub- 

 ject to washing. It is only when the washing has proceeded 

 far enough to cause a considerable fill and a young alluvium 

 forms that plants like the following appear: 



Salix nigra . Salix amygdaloides . 



Coreopsis palrnata. Bidejis fro7idosa. 



We have in this region an excellent illustration of a 

 mesophytic flora well established on the crest of hills. 

 Nearly all of the eastern slopes of the hills and the very 

 tops, east of the main line of bluffs, or those facing the 

 principal streams are covered with a mesophytic vegeta- 

 tion which does not differ essentially from those of the 

 older ravines. 



GRASSY HILLS. 



The loess mounds though made of a tenacious clay 

 show no springs or running water anywhere except in 

 the wooded canons at the base of the hills. The vegeta- 

 tion from early spring to fall is a succession of bloom, 

 beginning with such plants as 



Anemone patens var. Nuttalliana , Oxvtropis Lambertii , 

 CastiUeia s^ssiliflora, Lithospermum canescens. 



Lithospertnum angustifoliuni. 



Another common plant over the hillside is Comamlra 

 nmheJlata. Three weeks later the most conspicuous plant 

 over the loess mound is Si/mphoriatrpos occideufalis, which 

 is most abundant near the timber line, encroaching upon 

 the mounds. The Sijuiphoricarpos is a forerunner of shrubs 

 and trees at the edge of the loess mounds. Along with 

 it, frequently in great abundance, is the Verbena stricta 

 and the Fsoralea argophiilla, the latter with long roots. 

 The Lygodesmia jtincea, a typical xerophytic plant, is 

 extremely common, occurring not only in the vertical 

 clay banks but over the entire mound. 



Near the tops of the mounds Aplopappus spinulosus 

 forms broad masses. Quite widely distributed over 

 these loess mounds we have the Dalea laxijiora and the 

 D. alopecuroides, the former, with roots several feet long, 



