422 Tricotylous Races. 
ISOLATION OF TRICOTYLOUS RACES. 
HEREDITARY VALUES UF THE SECOND GENERATION. 
FIRST 
GENER- 1 5 10 15 20 25 30 35 40 45 50 55 60 65 
ATION 
Clarkia pulchella 16% 01171473421422 
rapaver R/weas 18% 002854 3 10001 
Papaver Rhoeas 19% 001 18214401 
Phacelia tanaceti folia 14^033113864222 
It is easily seen that in such cultures the choice of 
specimens which belong undoubtedly to the intermediate 
race is made possible. All plants with a low hereditary 
value are simply rejected, since the possibility exists that 
among them may be hidden hybrids between the two 
races. The high values are free from this doubt and 
indicate the pure race we are searching for. 
Thoroughbred races. Under this term those races 
are included in agriculture which have been considerably 
improved by stringent selection. In the first part of the 
first volume we have seen that they remain dependent 
on continued selection, and do not really become constant. 
For studying the features of such races, the tricotylous 
intermediate races afford most suitable material, for, 
after reaching the mean value of about 50%, we may 
select the extreme variants, and, by their culture, improve 
the race much farther. As instances I choose Mercurialis 
aiiuiia, a large agricultural crop, and Silene inflata, which 
I derived from seed introduced with cereals. Both cul- 
tures were started in 1892, and reached a hereditary 
value of 55% in the harvest of 1894. From plants with 
this value I raised a fourth generation, which offered me 
the following figures : 
