Aug. 7. 1910 Vegetative Succession Under Irrigation 749 



It is not surprising to find these meadow vetches appearing so early 

 when the numerous upland species are recalled, a proof of the upland 

 and lowland similarity as regards the soil and a further index to its char- 

 acter as pointed out in a preceding paragraph. Astragalus bodinii de- 

 velops long, spreading stems which make it difficult to harvest, but its 

 high nutritive value and the evident relish with which it is eaten over- 

 come this drawback. Though its development may be arrested, it will 

 ultimately form a large part of the hay crop. 



The other species, A. hypoglottis, does not seem able to hold its own 

 long where .4. Bodinii is present, and the latter will eventually largely 

 replace it. 



Oxytropis deflexus belongs to a different habitat and is to be regarded 

 here as a stray. It may be poisonous, but it rarely occurs in any abund- 

 ance. 



Such, then, is the condition of vegetation at the end of the first season. 

 During the second season one of two possible lines of development become 

 definitely established. Either the forming meadow enters upon what 

 may be called the Agropyron phase or else the Hordeum phase. As to 

 which phase appears depends on the following condition: It was ob- 

 served that the ranch company sometimes ran short of water; and in 

 such a case the newer areas were kept only moist, not wet like those 

 regions longer established, for which the greater part of the available 

 water was conserved. Granted that one or more of the wheat-grasses 

 happened to be dominant over a given area the year before (as was very 

 likely the case) a practically pure stand of this grass was the result (PI. 

 CV). The presence of an occasional tuft of Hordeum iubatum should be 

 noted. 



Before tracing through the development of this phase, the other possi- 

 bility should be mentioned. As a curtailed water supply was essential 

 to the dominance of Agropyron spp. at this time, so an abundance pro- 

 duced the Hordeum phase (PI. CHI, figure 1). This phase is more 

 strongly defined than the other because Hordeum jubatum is always the 

 dominant plant. Its chief competitor is Grindelia subalpina, which is 

 just as worthless and just as truly a weed. 



Here is striking evidence of the aggressive character of a plant which 

 because of its uselessness we call a "weed" and of the unobtrusive char- 

 acter of an indigenous and valuable grass. That is, the development 

 of the Agropyron association is primarily dependent on its local domi- 

 nance the preceding year. When such is not the case, the artificial condi- 

 tion described above tends to produce a mixed association characterized 

 by one or all of those plants which largely composed the upland and 

 the meadow elements, as discussed previously. Chief among these 

 will be Bouleloua oligostachya and Koelcria cristata, the two sedges Carex 

 siccala and C. stenophylla, Antennaria parvijolia, the meadow vetches 

 52169°— 16 3 



