312 THE FORMATION 



lests were made of a large number of species, and those selected which 

 showed a high per cent of germinability. Since this was the first experi- 

 mental 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 



Fig. 85. Heterochronous culture of Helianlhus annuus and Datura 

 stramonium. Family culture of Datura, Verbascum, etc., in tlie 

 foreground. 



were ruderal or subruderal. The species employed, and the kinds of cul- 

 tures in which they were grouped were as follows : 



1. Simple culture of Hclianthus annutis. The culture plot was tlivided 

 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, Panicuni rir^atuni, and Elynius 

 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. 



