METHOD OF CONTROL HABITATS 313 
4. Layered culture of Laciniaria punctata, Bidens frondosa, Salvia pitcheri, 
Cassia chamaecrista and Kuhnia glutinosa. Fifty seeds of each species 
were scattered more or less uniformly over the entire plot. 
5. Layered culture of Silphium laciniatum, Datura stramonium and Lac- 
tuca Iudoviciana. Fifty seeds of Datura and Lactuca, and 25 of Silphium 
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 Ocnothera rhombipetala (xerophytic), Verbascum 
thapsus (mesophytic), and Penthorum sedoides (hydrophytic). One hun- 
dred seeds of Oenothera and 200 each of Verbascum and Penthorum were 
scattered over the plot. 
7. Heterochronous culture of Helianthus annuus 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, Kuhnia, Panicum, Bidens, Onagra, 
Datura, Penthorum, Solidago and Verbascum. The plot was divided into 
g squares and in each were sown 50 seeds of one of these plants. 
9g. 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. 
1CLEMENTS, F. E. The Development and Structure of Vegetation, 166. 1904, 
