4 PERIODICAL OPENING AND CLOSING OF FLOWERS. 



rays of the sun, or the duration of their action. The temperature 

 and clearness of the air, in consequence of their evident influence 

 on the progress of the phases under observation, were regularly 

 noted. The temperature was marked by two thermometers of 

 the same range, one of which was exposed to the direct rays of 

 the sun, while the other hung in the shade. That which was 

 placed in the sun was either in a blackened hollow ball of brass, 

 or in a blackened cylinder of the same metal. The differ- 

 ence between the two thermometers was carefully recorded, as 

 affording an exact measure of the degree in which the flowers had 

 been exposed to the direct rays of the sun. The quantity of 

 moisture in the air and its barometrical pressure, as distinguished 

 from that of dry air, were not so constantly registered as of only 

 secondary influence. For the same reason the temperature of the 

 soil was generally neglected, and the more especially as the 

 plants were under artificial circumstances, from which no safe 

 conclusions in that respect could be formed. 



The number of species observed amounted to 140, belonging to 

 29 different orders of plants, of very different degrees of affinity. 



The results of the observations appear under the following 

 heads : — 



1. Phases exhibited by flowers. 



2. Dependence of the degree of expansion on temperature. 



3. Insolation, or exposure to the direct rays of the sun. 



4. Dependence of the sleep of plants upon the colour of their 

 corolla. 



5. Dependence of the same on the natural orders to which 

 the species belong. 



1. Phases exhibited by flowers. — If the duration of the sleep of a 

 plant be reckoned from that hour at which the blossom has 

 closed, as far as the mean daily expansion, to that when it has a 

 second time opened to the same extent, extending over the 

 minimum of the phase, we have the following results : — 



Number of species. Duration of sleep. 



2 10 hours. 



2 11 „ 



10 12 „ 



16 13 „ 



16 14 „ 



18 15 „ 



10 16 „ 



5 17 „ 



Mammillaria polytliela . 1 18 „ 



Scorzonera laciniata . 1 19 „ 



2 20 „ 



