THE QUADRAT METHOD IN TEACHING ECOLOGY 273 



six feet. Although only an occasional specimen of Distichlis 

 was to be seen, the soil contained three distinct strata of its 

 abundant and well-preserved rhizomes at depths of 13, 9, and 6 

 inches respectively. These indicated successive overflows and 

 deposits. Above these the soil w^as filled with a dense network 

 of the rhizomes of Agropyrum repens. However, only a few of 

 these plants were still alive, the soil being almost completely 

 occupied by alternate areas of Sporohohis longifoliussind Bulhilis 

 dactyloides. 



On the ecotones between the several plant zones in the 

 above areas (fig. 2) several quadrats were permanently staked 

 out, photographed and charted in the fall of 1916. Since more 

 striking changes take place yearly among the annuals^ — Dondia 

 smd Atriplex — than in the more stable grass zones, a few quadrats 

 in areas occupied largely by the former species are chosen for 

 illustration here. 



Quadrat 5 was located in such an area that it included bare 

 alkali flat, a narrow zone of Dondia, and extended into the 

 Atriplex area (fig. 2). Photographs of this quadrat taken in the 

 fall of 1916, 1917, and 1918 respectively are shown in figure 4. 

 The rank growth of Atriplex is due to a depression through which 

 surface water drains after rains. The soil on either side is more 

 salty. A study of these figures together with the chart quadrats 

 in figure 5 reveals a number of interesting changes. One of the 

 most striking is the almost total disappearance of Dondia in 

 1917 with the advance of Atriplex far out into the fonner Dondia 

 area. A count made on June 1, 1917, showed at that time 63 

 and 289 Dondias respectively in the first two decimeter rows of 

 the foreground, while the next two consisted of 966 Dondia 

 and 169 Atriplex, rather evenly distributed. What caused this 

 practically 100% mortaUty of Dondia in this portion of the 

 quadrat and the dominance of Atriplex is a question which the 

 student at once appreciates, and can only be solved by visits to 

 the field during the growing season. The drought during July 

 when only 0.56 inch of the 4.01 inches precipitation normal for 

 that month occurred was probably the time of greatest mortality. 



The thin stand of Atriplex, its small stature, and its presence 



