18 PERIODICAL OPENING AND CLOSING OF FLOWERS. 



the atmosphere is lost, and therefore some other cause than the 

 decreasing sunlight is at work in closing the flowers, which does 

 not depend on any diurnal period. 



Plants which close their hlossoms at or hefore sunset : 



Sonchus asper, 11 hours = — 11 

 Lactuca scariola ... — 9 

 Scorzonera laciniata . 



4 species 



5 

 12 

 10 

 13 

 13 



— 7 



— 6 



— 5 



— 4 



— 3 



— 2 



— 1 

 



Sunset then, like suni'ise, is no decisive element in the question, 

 for the number of flowers which close is far less at that hour than 

 some hours earlier. As, however, the sun advances in its coui'se, 

 the number of plants which fall asleep increases. 



Plants which close their blossoms after sunset : 



2 species +1 



4 „ ......+ 2 



Gentiana cruciata . . . + 3 

 Pyrethrum corymbosum . + 6 

 GEnothera biennis . . . +10 

 Lychnis vespertina . . +11 



A few hours after the insolation has begun in the morning, 

 the corolla of most plants is expanded, others begin to close as the 

 insolation becomes more intense, while a few still expand. After 

 mid-day the number of closed blossoms rapidly increases when 

 the insolation has reached its maximum. With the exception of 

 night-bloomers there are no plants whose cup has not been 

 expanded, and is now rapidly closing. As the insolation declines, 

 the number of closing blossoms increases, and becomes small at 

 the moment of the cessation of insolation. Later in the day, the 

 number of blossoms which close is from hour to hour nearly 

 equal ; neither the decrease of intensity of diffused light, nor the 

 departure of the sun, nor the far less intensity of twilight, seems 

 to have any influence on the law of the decrease of the number 

 of closing flowers. 



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

 — Those plants, the progress of whose phases can be graphically 



