356 CARNEGIE INSTITUTION OF WASHINGTON. 



S. eminens from Berkeley, California, and of several species of Aristida 

 and Bouteloua from Tucson, have been made at Lincoln, together with 

 their reciprocals. 



Most of the preceding species, together with Aristida purpurea, 

 Bouteloua hirsuta, Stipa comata, S. viridula, and Liatris punctata, have 

 been seeded at the five permanent stations. This has been done in 

 three different ways in order to permit an exact analysis of the results. 

 In the first method, the seed was sown on the surface and only slightly 

 covered with debris, thus simulating conditions in nature and sub- 

 jecting the seedlings to both root and shoot competition from existing 

 vegetation. In the second, seed was sown at the proper depth in a 

 trench 3 or 4 inches wide, from which the sod had been removed to a 

 depth of 4 inches and the soil replaced in a mellow condition. This 

 made germination more certain and did away with root competition 

 until the seedlings were established, but did not seriously modify aerial 

 conditions. In the third method, areas 0.5 meter square were denuded 

 to a depth of 3 or 4 inches and the sod replaced by fine soil in which the 

 seed was planted. Seedlings were also grown in adjacent tilled areas, 

 primarily for the purpose of studying root development. 



The season has been very favorable for plant growth, but consider- 

 able mortality among seedlings, even during short periods of drought, 

 emphasized the difficulties of ecesis and showed strikingly the effect 

 of environment and competition in selecting the plant populations in 

 the several habitats. While the unusual moisture greatly favored the 

 growth of the transplants in the salt flats, it resulted in the lack of 

 sufficient aeration for the growth of many transplants in the wet 

 meadow. Certain species prove able to grow but not to reproduce in 

 their new habitat; others are being replaced by the invasion of former 

 dominants, while differences between the plants in the original and the 

 new habitat are indicated by the various degrees of growth and repro- 

 duction. 



To obtain the fullest results from these studies, such as the compara- 

 tive equivalence of dominants of different associations, the conditions 

 under which extral dominants are adopted into the association, and the 

 outcome between dominants and subdominants, and between sub- 

 dominants alone, it is planned to continue the studies through a series 

 of years. However, the results already obtained serve to indicate 

 the relative importance of migration, physical factors, competition, and 

 biotic influences, such as grazing animals, rodents, etc., in affecting the 

 invasion of dominants and the permanence of communities. It seems 

 certain that the use of transplant and seed areas must come to be 

 regarded as indispensable for adequate and objective vegetation 

 studies. The indicator value of such work is obvious, and it is being 

 increased by correlating it not only with native plant production, but 

 also with the production of crop plants. 



