The standard evaporimeter represents nearly the proportion of 

 evaporation in the sandy loam fields. The surface was sprinkled with 

 a little loose sand which had drifted from the steep lee slope of the 

 near-by river dune. The bottomland stations were flooded during the 

 first part of the experiment; but this probably did not materially affect 

 the reading. The sand-prairie associations tested were at the Devil's 

 Hole, and the forest stations were in the woodland strip just east of 

 there. The mixed forest at this point had not nearly reached the ad- 

 vanced stage of the mixed forest of the marginal dune. An evaporim- 

 eter placed there would doubtless show a very low coefficient. The 

 coefficients in the above table vary directly as the openness of the as- 

 sociation. The evaporation in one of Transeau's most open associa- 

 tions,' a gravel slide, was a little more than three times the evaporation 

 in the mesophytic forest of Long Island. The evaporation in the Ha- 

 vana blowout is more than four times that of the mesophytic forest at 

 Havana. The blowout is probably more exposed than the Long Island 

 gravel slide.* The moisture relations in the Illinois sand areas may 

 be summarized in the statement that the water supply is ample, and 

 that the evaporation depends not so much upon the soil as upon the 

 plant-covering. 



The dry surface layer of the sand, in addition to its property of 

 retarding evaporation, has another and more direct effect upon plant 

 and animal life. This layer is practically sterile ; seeds can not germi- 

 nate in it, and must be buried. Certain plant seeds (as those of 

 Cenchrus) are armed with hooks or spines, perhaps to hold their posi- 

 tion in the sand and keep from blowing about on the surface. These 

 may later be buried by blowing sand and genninate. Other seeds 

 {Aristida tuberculosa and Stipa spartea) are able to bury themselves, 

 and round seeds have some chance of settling beneath the surface 

 (Gleason, 'lo: 93). Roots of plants do not branch out until they get 

 below the layer of dry sand. Burrowing animals usually stay beneath 

 the surface layer, which in other soils usually teems with life. To 

 prevent their burrows from caving in, insects and spiders usually line 

 the mouths with silk. 



Wind in the sand regions is one of the most important factors. 

 Its carrying power is selective in its action, sorting the sands accord- 

 ing to the size of its particles. The blowing of the sand results in 

 continual change of the surface topography, and plants which live 

 under these conditions must be able to resist burying or undermining. 



*The writer knows of no evaporation experiments in which readings in for- 

 ests have been taken above the tree canopy. Comparisons between open and forest 

 associations will not be complete until this has been done. 



