Aug. 7, 1916 Vegetative Succession Under Irrigation 745 



stock because of poisons they contain. The latter is peculiar in its habi- 

 tat relations. It appears in drier parts of meadows that have been 

 established for several years, but does not seem to stand the sudden 

 change to meadow conditions. This may be explained by the fact that 

 it grows in the lower parts of the draw, where the change in moisture 

 content becomes greatest. When it later invades the meadow, places 

 frequently exist that more nearly conform to its usual habitat. At any 

 rate, the new meadows are free from it for some time. 



CHARACTERISTIC BENCH-SLOPE PLANTS 



Agropyron Smithii Rydb. 

 Elymus condensatus Prsl. 

 Delphinium Menziesii DC. 

 Arabis hirsuta Scop. 



Potentilla pen-nsylvanica L., var. strigosa 



Pursh. 

 Astragalus spp. (three species). 

 Solidago concinna A. Nels. 



The change from upland to lowland is very abrupt, as shown in 

 Plates XCI and C, figure 1. The conditions are in many respects similar 

 to those of the preceding region, except that the water supply is greater 

 and even more constant. This permits the growth of various mesophytic 

 herbs and shrubs (for lists of these see pp. 757-758.) The upper part 

 of the slope is more or less like the bench, depending upon the local varia- 

 tion in the abruptness of the incline. Therefore the bench-slope plants 

 can not be satisfactorily segregated from those of other units, since 

 species characteristic to them find within the borders of the bench slope 

 entirely suitable habitats. 



Agropyron Smithii prefers a more constant water supply than its rela- 

 tives, so it is placed here, though a complete list o* the plants of either of 

 the complexes previously discussed would contain it. Elymus conden- 

 satus likes a moist, sunny, well-drained situation; consequently it is out 

 of the question as a meadow plant and is not of much value under any 

 condition, being coarse and woody. Delphinium Menziesii no doubt is 

 poisonous, but its numbers are ordinarily so limited that its interest 

 lies chiefly in the fact that it is a relative of Delphinium Geyeri. Ara- 

 bis hirsuta at times acts very much like a weed. One of the three 

 vetches at home here is Astragalus tenellus, the only upland vetch in 

 the new-meadow development. 



METHOD OF IRRIGATION USED 



Before considering the transition itself — that is, the artificial trans- 

 formation of upland to meadowland — the reader should know something 

 of the mechanical means employed. Although the ranch owners have 

 taken some pains to build large reservoirs, such as the one shown in 

 Plate CI, figure 2, the actual distribution of the water over the land is 

 accomplished in the crudest way imaginable. A ditch is built along what 

 is obviously the highest ridge of a given area and provided with the 



