The Isolation of Tricolyloiis I iilcnncdiafc Races. 439 



these plants 25 set seed, Init the culture was iinsueeess- 

 ful in this year, owing to adverse circumstances, and 

 only a few of the plants produced more than 200 fertile 

 seeds. The values, therefore, were not very exact, but 

 formed a close group ranging between 18 and 56%, 

 with a mean of 32%. It will be seen that in spite of the 

 selection a general retrogression had taken place. 



Suunnary. If we look at the results of the experi- 

 ments which have been described, we are struck by the 

 fact that a certain group of hereditary values appears 

 much more commonly than others. These are the fig- 

 ures ranging round 55%, and this value is usually 

 reached at the conclusion of the second generation or, 

 in less favorable experiments, at the conclusion of the 

 third or fourth. A\'ith a view to emphasizing this fact 

 I have grouped the whole series of experiments in such 

 a way that the figures round 55% are brought together 

 in one column : 



ISOLATION OF TRICOTYLOUS INTERMEDIATE RACES. 



HIGHEST HEREDITARY VALUES EXPRESSED IN PERCENTAGES FOR THE 



SUCCESSIVE GENERATIONS. 



Anfirr/iinujn tnajus . 

 Mercurialis annua . 

 Silcne in flat a . 

 Cannabis sativa . 

 Clarkia pulchella . 

 Helichrysiiin bracteaiurn 

 Papaver Rhoeas . 

 Phacelia tanacetifolia 

 Oenothera hirtella 



FIRST GEN- 

 ERATION 



1892 

 1892 

 1892 

 1893 

 1895 

 1895 

 1895 

 1895 

 1895 



1-50' 



7 

 I 

 I 

 I 



8 

 

 3 

 3 

 I 

 I 

 I 



25 

 2 

 32 

 15 

 16 

 41 

 20 



— 1 I ' 14 



I i 8 



ABOUT 



55 9r 



41 

 55 

 55 

 52-63 

 64 

 51 

 56 

 58 

 56 



60-95 fr 



79 

 86 

 73 

 80 

 79 

 52 

 75 

 90 

 89 



79 

 92 

 56 

 90 



91 



In this table the first column gives the year in which 

 the experiments began, either with the selection of tri- 



