8 PERIODICAL OPENING AND CLOSING OF FLOWERS. 



It appears then that at the inferior culmination of the sun the 

 night-bloomers are most expanded ; that the expansion decreases 

 as the sun approaches the horizon ; that at suurise they close, 

 when the day-bloomers commence their phases, being most 

 expanded at midday, and closed again towards sunset, when the 

 night-bloomers in turn recommence their course. 



From these tables it is clear that the phenomena of flowers, so 

 far as they relate to the sleep of plants, and the diurnal periodical 

 change in the state of the blossoms, are in close causal connection 

 with the apparent daily course of the sun, and therefore its 

 insolation and diurnal variation must be regarded as the proximate 

 cause of the diurnal periodical return of the interchange between 

 6leep and waking. 



The next point which engages our notice is the connection 

 of the duration of sleep with the epoch of the greatest 

 expansion . 



The author,* in another treatise, had proposed certain laws as 

 regulating the sleep of plants. The first is as follows : — " In those 

 blossoms which are fully expanded in the morning, the duration 

 of expansion is short." New observations have afforded the 

 following results with respect to those flowers which are fully 

 expanded from 12 p.m. to mid-day : — 



The mean duration of sleep in forty-one species which expand 

 in the morning is 148 hours, that is, 08 greater than the mean 

 duration of sleep in eighty-six species for which the duration of 

 sleep has been determined without respect to the diurnal epoch 

 of the maximum change. In twenty-six species the duration is 

 greater, and only in sixteen species less than 14 2. The law is 

 therefore strengthened by a multiplication of observations. 



A second law was, " In those plants whose blossoms expand in 

 the afternoon, the condition of waking is limited by the duration 

 of the physical day, or the length of time the sun is above the 

 horizon." 



* Abk. der. Km. Ocsell. der Wissenschafien, V. Folye, 4 Band. p. 83. 



