April, 1919] 



Beginnings of Revegetation 



331 



The results of these tests showed clearly that in all sorts of 

 habitats there was a considerable margin of available moisture, 

 even at the close of an unprecedented drought. 



PREFERENCE FOR WET PLACES POSSIBLY DUE TO CONCENTRATION 



OF SALTS. 



But in spite of this it could not be questioned that the rankest 

 growth occurred in the wettest places. Calamagrostis langsdorfii, 

 for example, which in normal country thrives best on well 

 drained mountain sides, has here reached its full growth only 



Photograph by Robert F. Griggs 



SEEDLINGS, MOSTLY CAMPE BARBAREA, STARTING IN A 

 WET PUMICE FLAT. 



in springy places where the water is so abundant as to stand 

 on the surface. (See page 332). For a long while it was very 

 much of a puzzle why it did not spread onto the adjacent 

 ground, whose soil-water content is more similar to that of 

 the habitats it usually occupies. But finally an explanation 

 .suggested itself because of the similarity of conditions in these 

 places to the alkali spots on the prairies. Everyone familiar 

 with such a region as the Dakota prairies has noticed that 

 such springy places become covered by a heavy crust of alkali 

 salts, left behind from the evaporation of the seepage water. 

 The places occupied by the plants in question present exactly 



