Research methods in ecology

by Frederic E. Clements

Fig. 84. Mixed culture of Solidago rigida and Onagra 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, germination tests 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 of Helianthus annuus and Datura stramonium. Family culture of Datura, 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 of Helianthus and Panicum were planted alternately at equal distances in one-half of the plot, while the other half was planted similarly with Helianthus and Elymus.

3. Mixed culture of Solidago rigida and Onagra biennis. Over one-half of the plot were scattered 50 seeds of Solidago and 100 of Onagra; 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 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 Oenothera rhombipetala (xerophytic), Verbascum thapsus (mesophytic), and Penthorum sedoides (hydrophytic). One hundred seeds of Oenothera and 200 each of Verbascum and Penthorum were scattered over the plot.