PERIODICITY IN 



WITH 



WORK 



BY C. H. DANFORTH. 



The fact that there is a certain periodicity in the appear- 

 ance of reproductive phases of many algae is a matter of 

 common observation, and several attempts have been made to 

 determine more or less definitely the factors controlling re- 

 production in these forms. In work of this kind Spirogyra 

 has perhaps been the most frequent subject for experimenta- 



observation, but the work of Williams ( 



and 



Hoyt ('07) on Dictyota has yielded interesting, if somewhat 

 puzzling results. The 



former 



and clearly marked periodicity 

 1 he found to liberate the eggs 



sperm 



of each cycle. An analysis of the conditions that vary con- 

 comitantly with the tide, and the fluctuations in the tide and 

 time of sexual maturity of Dictyota on the various pt 



erved 



periodicity in the reproduction of this plant is controlled by 

 the amount of light received, which in turn is regulated by 

 the tides. Nevertheless plants kept in an aquarium were 

 found to show the same periodicity the following spring 



had 



from 



Williams therefore concluded that the periodicity mani- 

 fested by Dictyota dichotoma is an inherited characteristic 



comes 



Hoyt 



* The work recorded in this paper was done in the graduate labor- 

 atories of the Henry Shaw School of Botany at the Missouri Botanical 

 Garden and the author's acknowledgments are due Professor George 

 T. Moore for suggestions and assistance. 



(49) 



