Conjugation of Life History of Spathidium spathula 303 



156 (1738) 



The survival value of conjugation in the life 

 history of Spathidium spathula. 



By LORANDE LOSS WOODRUFF and HOPE SPENCER. 



[From the 0 shorn Zoological Laboratory, Yale University .] 



In a former communication it has been shown that in our 

 pedigree cultures of Spathidium spathula, exconjugant lines, in the 

 great majority of cases, exhibit a higher rate of division during 

 the first fifteen days than the parent; lines. 1 The purpose of the 

 present paper is to summarize briefly the results to date with 

 respect to the effects of conjugation as exhibited later in the life 

 history of the pedigree lines. 



1. Conjugation in the majority of cases increases the length 

 of life of the exconjugant line, so that it lives after the death of 

 the parent so-called "non-conjugant" line. This is shown by 

 the fact that of forty-seven excqnjugant lines, thirty lines lived 

 longer; four lines lived to essentially the same date; and thirteen 

 lines died before their respective parent lines. 



2. The total number of generations attained by the exconjugant 

 exceeds those attained by the parent from the date when the ex- 

 conjugant arose to the death of the parent in about eighty 

 per cent, of the lines. Of fifty-two comparable lines, forty-one 

 lines exceeded their respective parent lines in number of fissions; 

 two practically equalled; and nine lines did not attain so many 

 generations. The fact is evident that conjugation increases the 

 number of fissions to a total which could not otherwise have been 

 reached. 



3. If the period be considered during which both lines were 

 alive, the results are even more conclusive. Forty-four lines at- 

 tained more generations than the parent; four equalled the parent; 

 and four completed a smaller number of fissions. Thus over 

 eighty percent, of the exconjugant lines attained more generations 

 than their respective parent lines. 



1 L. L. Woodruff and Hope Spencer, Proc. Soc. Exp. Biol, and Med., 1921, 

 xviii, 240-241. 



