312 THE FORMATION 
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 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 Helianthus annuus and Datura 
stramontumn. Family culture of Datura, Verbascum, etc., in the 
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 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 so seeds of Solidago and 100 of Onagra; over 
the other, 100 and 200 seeds respectively. 
