METIIOD OF CONTROL HABITATS 311 
the species are of very different height. Thus, rosettes have been grown 
with stemmed plants, tall slender forms with low branching ones, erect plants 
with twining and climbing plants, etc. Further evidence as to the nature 
of competition has been sought by means of ecad cultures, and factor cul- 
tures. In the former, plants of different response to water and light are 
grown together under the same conditions, in order to evaluate the part 
played by the nature of the plant. In a factor culture, the area is divided 
-into two or more parts which are given different amounts of water or of light, 
in order to determine the influence of slight variations upon the same com- 
petitors. In somewhat similar fashion, an attempt has been made to 
Fig. 84. Mixed culture of Solidago rigida and Onagra biennis. 
ascertain the bearing of biotic factors upon competition. Cultures are 
easily made in which Cuscuta or parasitic fungi are used to place certain 
species at a disadvantage. Permanent cultures are obtained by allowing the 
plants to ripen and drop their seeds for several generations, just as in 
nature. ‘They are indispensable for determining the final outcome of the 
competition between different species. 
362. Details of culture methods. All competition cultures have been 
made 1 meter square. In other words, they are quadrats, and they are 
treated exactly as denuded quadrats in the field with respect to factor 
readings, charts, and photographs. In the writer’s studies, germination 
