METHOD OF CONTROL HABITATS 313 



4. Layered culture of Laciniaria punctata, Bidens frondosa, Salvia pitchcri, 

 Cassia clianwccrista and Kiihnia glntinosa. Fifty seeds of each species 

 were scattered more or less uniformly over the entire plot. 



5. Layered culture of Silphinm laciniatum, Datura stramonium and Lac- 

 tnca Indoviciana. Fifty seeds of Datura and Lactuca, and 25 of Silphinm 

 were sown uniformly in one-half of the plot. In the other half, 25 holes were 

 made at equal intervals, and one seed of each of the three planted in each 

 hole. 



6. Ecad culture of Oenothera rhombipetala (xerophytic), Verbascum 

 thapsus (mesophytic), and' Penthorum sedoides (hydrophytic). One hun- 

 dred seeds of OenotJicra and 200 each of Verbascum and Penthorum were 

 scattered over the plot. 



7. Hetcrochronous culture of Heliantkus annnus and Datura stramon- 

 ium. One hundred seeds of Helianthus were scattered over one half, and the 

 same number of Datura seeds over the other half of the plot. In both, 

 also, 50 seeds were sown in one 4-inch circle, and 25 seeds in a second circle 

 at some distance. A month later, 100 seeds of Helianthus were sown in 

 the Datura plot, and vice versa. 



8. Family culture of Helianthus, Kiihnia, Panicum, Bidens, Onagra, 

 Datura, Penthorum, Solidago and Verbascum. The plot was divided into 

 9 squares and in each were sown 50 seeds of one of these plants. 



9. Community culture. The sowing was made exactly as for the family 

 culture, except that 20 seeds of each plant were used. In the middle of 

 each square, 5 seeds of a different species were planted. For the Helian- 

 thus, Kuhnia, and Panicum groups, Onagra was used ; for Bidens, Onagra, 

 and Datura, Helianthus was used, and for Penthorum, Solidago, and Ver- 

 bascum, Panicum. 



At the time the cultures were started, check plants were sown in pots. 

 The most vigorous seedlings were transplanted singly to large pots, and 

 grown under conditions of water, light, and soil as similar as possible to 

 those of the competition plots. Photographs of check plants and plots were 

 made at the proper intervals, and the plots were charted in quadrats to show 

 the course of competition. The factors which control competition were 

 sought in a critical study' of water-content and light values, which is still 

 in process. This work has gone far enough to indicate the correctness of the 

 view^ that competition is purely physical in character. It has, moreover, 

 been demonstrated that "room" in competition is merely a loose expression 

 for the relation between the number of individuals in a given space, and the 

 amount of water, light, and temperature available in the same space. 



^Clements, F. E. The Development and Structure of Vegetation, 166. 1904, 



