160 



EARL E. SHERFF 



25 cm., 1.5 cc; at 107 cm., 2.7 cc; at 175 cm., in the uppermost 

 stratum, 6.4 cc, — or just 1000 % as great as at the soil surface. 

 These differences in the rates among Typha were strongly accent- 

 uated because the readings were taken in autumn, when many of 

 the Typha leaves had started to wither and bend over, thus gi\dng 

 greater exposure in the upper strata and greater shelter in the 

 lower. Then, too, numerous plants of Scutellaria galericulata, 

 Teucrium occidentale, Polygonum Muhlenbergii, etc., absent 

 among Phragmites, were present among Typha and acted as a 

 further check to evaporation in the lower strata (in which, to a very 

 great extent, they vegetated). 



The data plotted in figures 3 and 4 corroborate very emphatically 

 those of Yapp,^ who found that during a total of about fifteen 

 days, the evaporation rate just above (not, as at Skokie Marsh, 

 in the upper strata of) tail "sedge vegetation" was over 1500 % 

 as great as it was at 12.5 cm. above the soil surface. They con- 

 form likewise ■v^dth the more recent results of Dachnowski^ who 

 obtained during about five days, at a height of 150 cm. in an .Amer- 

 ican bog, an evaporation rate 200 % as great as at a height of 

 7.5 cm. Obviously, we must conclude wdth Yapp, that plants 

 may grow in proximity to each other and yet, if vegetating in 

 different strata above the soil surface, be subject to wi(iely differ- 

 ent growth conditions. Thus, for example, Riccia natans and 

 Typha latifolia may be found together in great quantity, but 

 they vegetate mostly in different atmospheric strata and hve 

 under evaporation conditions much more different than do Teu- 

 crium occidentale (of the reed swamp) and Aster salicifolius (of 

 the swamp white oak- white ash forest), plants of similar height 

 and growth form. 



Acknowledgement is made of the writer's indebtedness to Mr. 

 George D. Fuller, of the University of Chicago, for many helpful 

 suggestions during the progress of the work described here. 



' Yapp, R. H., On stratification in the vegetation of a marsh* and its relations 

 to evaporation and temperature. Annals of Botanj- 23: 275-320. 1909. 



' Dachnowski, A., The vegetation of Cranberry Island and its relations to the 

 substratum, temperature and evaporation. Bot. Gaz. 52: 126-150. 



