THE QUADRAT METHOD IN TEACHING ECOLOGY 



271 



depth. This gave presumably a rather equal distribution of the 

 salts.2 



The distribution of the alkali in the various plant communities 

 is shown in the table. 



* In the table, sodium and pota.ssium are given together. There are varying 

 amounts of the two metals though most of the mixture consists of sodium. 

 In the calculations only sodium has been considered and the sodium oxide and 

 sodium carbonate have been calculated from the weight of sodium and potassium 

 as if only sodium was present. 



The table at once reveals the salt content as the controlling 

 factor in the distribution of the vegetation. Usually Salicornia 

 herbacea accompanies or even precedes Do7idia in the saltier 

 places but it was not present in the area under consideration. 

 It grows in wet spots on the floor of the basin, in the saltiest of 

 soil, often growling through a crust of salt and is frequently the 

 sole inhabitant. (Cf. figure 3.) Corispermum hyssopifoliiim 

 frequently occurs with Atriplex or covers areas exclusively where 

 the situation is subruderal. 



The area occupied by these halophytes is alluvial wash where 

 the salt has been deposited by successive overflows year after 

 year. Formerly it was much more extensive. The halophytes 

 are rapidly being replaced by other species and by crop plants 

 as the soil becomes less salty due to better drainage resulting 

 from the straightening of stream courses. The replacement of 

 salt grass by prairie species is often clearly marked. Agropyrum 

 repeiis is often the first invader and is followed by Sporoholus 

 longifolius, Panicum virgatnm, Andropogon furcatiis, and other 

 prairie species. An interesting successional sequence w^as de- 

 tennined while making a bisect in a rich alluvial flood plain 

 where the water level occurred in gumbo soil at a depth of about 



^ The writer is indebted to Professor C. J. Frankforter of the department of 

 chemistry for these determinations. 



