CONJUGATION AND ENCYSTMENT 353 



stock became very weak toward the close but it did not die out, 

 and, of course, it is not known how much longer it would have 

 survived. The fact that it continued so long without conju- 

 gation or encystment seems to indicate that neither of these 

 processes is necessary for continued existence. 



This conclusion is in perfect harmony with what is known 

 regarding the life-history of many of the lower plants and with 

 the results obtained by Woodruff in very thorough and extensive 

 experiments on Paramecium. Woodruff's conclusion is, how- 

 ever, open to criticism. He says, after having obtained 3029 

 generations without conjugation ('12, p. 123): "I believe this 

 result proves beyond question that the protoplasm of a single 

 cell may be self-sufficient to reproduce itself indefinitely, under 

 favorable environmental conditions, without recourse to con- 

 jugation, and clearly indicates that senescence and the need of 

 fertilization are not primary attributes of living matter." That 

 the protoplasm of certain single cells is self-sufficient to repro- 

 duce itself without recourse to conjugation has, in my opinion, 

 long since been known, for nothing in the nature of conjugation 

 has ever been discovered in bacteria and in a considerable num- 

 ber of algae. . If this is true. Woodruff's results merely support 

 a well established conclusion regarding the necessity of conju- 

 gation for the continued existence of protoplasm; they make it 

 possible to add Paramecium to the fist of organisms in which 

 conjugation has been found not to be necessary for continued 

 reproduction. 



THE EFFECT OF CONJUGATION ON DEATH-RATE 



Jennings ('13, p. 293) found, in extensive and very thorough 

 experiments with Paramecium that ''Conjugation decreases the 

 rate of fission, causes a great increase in variation in fission rate, 

 brings about many abnormalities, and greatly increases the 

 death-rate." He concludes (p. 378), as previously stated, that 

 conjugation does not produce rejuvenescence but that it func- 

 tions in the production of new combinations which are better 

 adapted to the existing conditions than others and that these 

 serve to perpetuate the race while the others die out. 



