Fig. 84. Mixed culture ofSolidago rigidaandOnagra biennis.
Fig. 84. Mixed culture ofSolidago rigidaandOnagra biennis.
Fig. 84. Mixed culture ofSolidago rigidaandOnagra biennis.
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, germinationtests were made of a large number of species, and those selected which showed a high per cent of germinability. Since this was the first experimental study of competition, this test was deemed necessary, but it is quite evident that no such selection is made in nature. Consequently, when the seeds used are known to be fresh, a germination test is usually superfluous. Considerable care was taken also to select species known to be vigorous growers, with the result that practically all the species used for experiment were ruderal or subruderal. The species employed, and the kinds of cultures in which they were grouped were as follows:
Fig. 85. Heterochronous culture ofHelianthus annuusandDatura stramonium. Family culture ofDatura,Verbascum, etc., in the foreground.
Fig. 85. Heterochronous culture ofHelianthus annuusandDatura stramonium. Family culture ofDatura,Verbascum, etc., in the foreground.
Fig. 85. Heterochronous culture ofHelianthus annuusandDatura stramonium. Family culture ofDatura,Verbascum, etc., in the foreground.
1.Simple culture of Helianthus annuus.The culture plot was divided into four equal parts; 12 seeds were planted in one, 25 in another, 50 in the third, and 100 in the fourth.
2.Mixed culture of Helianthus annuus, Panicum virgatum, and Elymus canadensis.Twenty-five seeds each ofHelianthusandPanicumwere planted alternately at equal distances in one-half of the plot, while the other half was planted similarly withHelianthusandElymus.
3.Mixed culture of Solidago rigida and Onagra biennis.Over one-half of the plot were scattered 50 seeds ofSolidagoand 100 ofOnagra; over the other, 100 and 200 seeds respectively.
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 Lactuca ludoviciana.Fifty seeds ofDaturaandLactuca, and 25 ofSilphiumwere 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 hundred seeds ofOenotheraand 200 each ofVerbascumandPenthorumwere scattered over the plot.
7.Heterochronous culture of Helianthus annuus and Datura stramonium.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 ofHelianthuswere sown in theDaturaplot, andvice versa.
8.Family culture of Helianthus, Kuhnia, 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 theHelianthus,Kuhnia, andPanicumgroups,Onagrawas used; forBidens,Onagra, andDatura,Helianthuswas used, and forPenthorum,Solidago, andVerbascum,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[45]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.