158 Prof. Mayer's Observations on the 



1st, The growth was generally more accelerated during the 

 twelve hours of day, than during the twelve hours of night. 



2dli/, The growth was generally more rapid from eight in the 

 morning to two afternoon, than in the subsequent period of six 

 hours, 



Sdlt/, The growth of each plant presents daily two periods of 

 acceleration and two periods of retardation ; the first accelera- 

 tion shews itself between eight and ten in the morning, the se- 

 cond between noon and four. 



Thus when the total growth in length of a plant of barley 

 is 11"'.76 in the twenty-four hours, this increase will be distri- 

 buted periodically as follows : 



From 8 A. M. to 10 a. m. 



l.2T\ 



0.99 V3.45°-\ 



1.19J ( 



6.42 



\ 



2.97 



5.34 

 11.7'i 



The author also deduces from his table the means of the 

 total growth of each of the plants taken separately, from eight 

 in the morning to ten at night, and he estimates the means of 

 all these individual gi'owths during the same period at 0"'.80. 



The most remarkable circumstance which this series of ob- 

 servations and calculations presents, is without doubt the alter- 

 nate acceleration and slackenings which takes place three times 

 a day, in the morning, shortly after noon, and later in the even- 

 ing, as well as the relation which is observed in the intensity of 

 each acceleration, and of the slackening which follows it. The 

 greatest acceleration takes place from noon to four o'clock, and 

 is followed by the greatest slackening. The smallest acce- 

 leration takes place from six to eight in the evening ; and the 

 slackening which immediately follows it from eight to ten, is the 

 most imperceptible of all. 



Heat is with reason considered as the principal agent of all 

 regular vegetative growth, and we know that heat follows a re- 

 gular progress in its daily increase and diminution. Moisture, 



4 



