426 The Ohio Journal of Science [Vol. XIX, No. 7, 



about the middle of the forenoon and falls back to the normal 

 night rate at about noon, although the plants were under 

 conditions of constant temperature, saturation deficit, evapora- 

 tion and total darkness. 



A number of experiments were performed which show the 

 conditions under which this rhythm takes place. Tobacco 

 and mullein show a rhythm in the transpiration curve in total 

 darkness when preceded by a day of normal light conditions, 

 while moth mullein under the same conditions does not show 

 this rhythm. This rhythm in tobacco and mullein does not 

 take place on the second day in the dark room. In tobacco 

 this rhythm does not take place on the following day unless 

 the plant is placed in the dark room before noon. It seems, 

 therefore, that this rhythm is due to some definite internal 

 condition and that certain plants show it while others do not. 

 Different plants were used in each experiment and all the plants 

 of a given species agreed in their behavior. The cause of this 

 rhythm is most likely in stomatal activity, but because of the 

 large errors in measuring stomatal movements as compared 

 with the small movement that is necessary to produce this 

 rhythm this fact has not been satisfactorily established. 



CORRECTION. 



In the November, 1918, Journal of Science, Vol. XIX, 

 No. 1, p. 61, in the second paragraph and the second line of the 

 paragraph for the word "family" read "class Edrioasteroidea, 

 Billings." 



On page 77, in the next to the last paragraph, the citation 

 from Bather is a mistake of the author's. Mr. Bather does not 

 hold the views there ascribed to him. I have Mr. Bather to 

 thank for these important corrections. 



Stephen R. Williams, 



Miami University, 



Oxford, Ohio. 



Date of Publication, May 25, 1919. 



