388 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



showing an increase in the autumn. (5) The surface curve 

 I'loam) of the lowlands shows a higher water content than its 

 subsoil (sand). 



(b) Temperature. Grraphie data concerning the temperature 

 of the air (three feet above the earth) and surface soil (6 in.) 

 taken at 3 p. m. and 5 a. m. show that (1) the temperature of 

 the earth lags behind that of the air; (2) the lowland tempera- 

 tures range slightly below the upland. A series of temperatures 

 taken in the air three feet above the earth during the months of 

 April, May, June, July, August, September, October and No- 

 vember show that the temperature of the air is materially higher 

 than that of the soil; (3) The soil absorbs heat cum.ulatively and 

 gradually radiates it, the lower layers lagging behind the upper 

 in its absorption but retaining the heat longer. 



Plant formations. This prairie province may be said to com- 

 prise four formations: (1) Upland Prairie (2) ^Meadow (3) 

 Swamp (4) Pond. Every formation has a variety of local fac- 

 tors such as water content, soil and light, which give rise to 

 constantly recurring gToiips or associations in the presence of 

 the same conditions. The chief causes of difference in associa- 

 tions are their habitat features which ar^ not common factors. 

 The principal factors which are not common or which vary in 

 marked degi'-ee are (1) type of soil and (2) water content of 

 habitat. Structure of soil has a direct bearing on water con- 

 tent. Water content depends on the type of soil, drainage and 

 rainfall. 



Reversion takes place sloM^ly and is rare. A denuded soil usu- 

 ally does not survive the activities of certain introduced ruderals 

 such as blue grass. 



Succession. Evidence of invasion of the prairie by forest in 

 ravines or on moist slopes is not uneomj2ion though it seems 

 limited in progress and restricted to moist locations. 



LITERATURE. 

 Beyer, S. AV., Geology of Story County, Iowa: Iowa Geol. Survey, 



9, p. 155, 1899. 

 Clements, F. E., Research Methods in Ecology, Lincoln, Nebraska, 



1905. 

 FarloAV, W. G., and Atkinson, Geo. F., The Botanical Congress at 



Brussels: Bot. Gaz. 50, pp. 220-226. 

 IVIarean, H. W., and Jones, G. B., Field Operations of the Bureau of 



Soils, Soil Survey of Story County, Iowa, 5, p. 833, 1903. 



