540 H. S. Jennings and George T. Hargitt. 



43, together with the history for comparison, of four lines of the 

 similar race L2, on the same days and under identical conditions 

 in every respect. 



After all the eight lines of race 4-3 had thus died out, two more 

 individuals were taken from the general culture of 43 and eight 

 lines from them cultivated as before. These again all died out 

 after about half a dozen fissions. A third set of eight lines, from 

 two other individuals of race 43, had the same fate. 



Thus it is clear that the race 43, though living in a large culture 

 made from timothy hay and tap water, precisely like that in which 

 the other races are living, cannot be cultivated in slide cultures of 

 fresh hay infusion changed every day, though most of the other 

 races flourish under this treatment. It is apparently the continued 

 freshness of the infusion that destroys the individuals of race 45; 

 if the infusion is allowed to stand for weeks, with the decaying 

 stalks of hay, this race flourishes. 



Other illustrations of the fact that the different races are adapted 

 to different cultural conditions came to light in the experiments in 

 which races of different size were placed together in the same 

 culture vessel (see p. 516). Owing to the difference in size it was 

 easy to recognize the individuals of the two races in the mixture, 

 and in doubtful cases isolation and propagation, with measure- 

 ments of the progeny, gave absolutely certain determinations. 

 In many mixtures of this kind one of the races frequently died out, 

 after lapse of a considerable period, while the other race continued 

 to exist unchanged. Thus, k and i were mixed October 8, 1908; 

 on February 25, 1909, only k was found in the mixture. Again, 

 D and i were mixed October 21, 1908; on February 25, 1909, 

 only i was present. L2 and i were mixed March 10, 1909 ; in April, 

 1910, only ^ was found in the culture. Thus it is clear that the 

 different races are adapted to somewhat different conditions, so 

 that one often dies out while another flourishes. 



It may be noticed that if the fact had not been known that two 

 races of diverse size were present in these mixtures, then measure- 

 ments of those present would give very different results at the 

 beginning and at the end of the culture. This might readily be 

 attributed to the direct action of the environment, and if one of 



