PERIODICAL OPENING AND CLOSING OF FLOWERS. 



Hour of com- Duration 



plete expansion. of sleep. 



Passiflora ccerulea . . 5 p.m. 14 

 PyrethrumcoryrnbosumlQ „ 11 5 

 Oenothera biennis . . 11 „ 12 



The mean duration of sleep in twenty-seven species whose 

 flowers expand after midday is 12*9, that is, 1*3 less than the 

 normal duration. In those cases where the full expansion takes 

 place at mid-day, observations on fifteen species give a mean of 

 l4 - 2. The second law is therefore confirmed. 



A third is, " Those plants which expand at night seem never to 

 fall completely into the state of sleep." In the author's former 

 observations the duration of sleep was confined to those hours in 

 which no alteration takes place in the phases, whereas in the 

 treatise before us it is extended to the time at which the expansion 

 has attained its mean diurnal condition. The law therefore must 

 be stated in the following terms : — " In those plants whose 

 blossoms are fully expanded in the night, the duration of sleep is 

 the shortest." The mean duration of sleep in the three night- 

 blowing plants which have been so often quoted is ll - 8, that is, 

 less than twelve hours, and therefore the third law also is 

 established. 



The following list contains a comparative view of the duration 

 of sleep in flowers which open at different times of the day : — 



Morning bloomers (41 species) 14 "8 

 Mid-day bloomers (15 species) 14*2 



Afternoon bloomers (27species) 12 - 9 

 Night bloomers (3 species). . 11 "8 



A fourth law was laid down in the following terms : — " Those 

 blossoms which are fully expanded in the morning open in 

 general more rapidly than they close, while in those which open 

 in the afternoon the contrary law prevails." This will appear 

 from the following table : — 



