(20) 



Inheritance proved to occur by selection experimentc. 

 Selection experiir.eri ts 1 and 2 - Contradictory 

 results of two brief experiments in mass selection. In 

 order to bring out clearly the reasons which led me to 

 abandon mass selection for individual selection based on a 

 progeny test, it seerns worth while to give a brief account 

 of two experiments in mass selection which came to an abrupt 

 and unexpected end. The fii'st of these experiments was 

 ended by an epidemic of sexual reproduction, the second by 

 a period of extremely hot weather which probably acted in- 

 directly by accelerating the multiplication of undesirable 

 bacteria. 



Neither of these experiments lasted long enoxigh for the 

 application of the real test of their effectiveness, the 

 free multiplication of two altered strains in comparison 

 with each other, hut since selection consists only in al- 

 lowing certain individuals to breed ar:d denying that pri- 

 vilege to others, a good idea of whether selection is 

 being effective car. be gained by com.paring the average 

 spine number of the progeny produced by high- and low-se- 

 lected groups during the same period. Such comparisons 

 for selection experiments 1 and 2 are given in Tables V 

 and VI. 



Selection experiment 1. Table V shows the progressive 

 effect of selection in a small many-spined clone closely 

 resembling line 30. The progenitor of this race was iso- 

 lated from algae taken from the Homewood pond on October 

 8,1914. On November 9, 52 individuals had been secured by 

 the multiolication of the original one, and selection 



