328 H. S. JENNINGS 



level shown by the other set K of table 32. In spite of the utmost 

 care, and the division of the lines as soon as possible, so as to have 

 more than one from each of the ex-conjugants, the progeny of 

 three of them had died out within eight days, and a fourth died 

 out later. Only two of them survived till September 7, when this 

 experiment was discontinued; and the nine lines derived from 

 these two were then multiplying much less rapidly than those 

 derived from set K (table 32). It should be stated further that 

 two tests made respectively three and four months later (one 

 December 1, 1910, the other January 7, 1911), showed that the 

 members of set K (conjugants of June 3) were still far more 

 vigorous than conjugants of August 10 (set D 1). In the test 

 comparison of December 1, all the twelve lines of set D 1 (con- 

 jugants of August 10) died out after a week of cultivation on 

 slides, while those of set K flourished. 



When however we compare the records for the conjugants of 

 August 12 (set D 1) with those for the non-conjugants of the 

 same culture (set D 2) in table 32, we find that the conjugants 

 have a decided advantage. The non-conjugants ceased multi- 

 plication almost entirely, after the first week, and gradually died 

 out, the last one dying on September 7. At this time the descend- 

 ants of two of the ex-conjugants were multiplying well, so that 

 an indefinitely large number of progeny were later produced 

 from them. 



Thus in this case two of the six conjugants were more vigorous 

 than any of the non-conjugants of the same stock and cultural 

 history. Most of the conjugants died out, but in the natural 

 course of events the entire set would have been replaced by the 

 progeny of the few more vigorous lines. 



This is the only case, out of a very large number of experiments, 

 that gives any indication of a beneficial effect of conjugation on 

 vigor and survival. Just what has happend here? First, atten- 

 tion should be called to the fact, already set forth, that conjuga- 

 tion in this depressed stock was very scanty; in connection with 

 the further fact that the condition for producing conjugation is a 

 period of rapid multiplication, followed by a check. Now, from 

 this and from the data of tables 18 and 19, it is evident that there 



