16 PERIODICAL OPENING AND CLOSING OP FLOWERS. 



intensity. The author's observations were made in a position 

 where the insolation did not begin till three hours after sunrise. 

 Plants which wake after sunrise : 



9 species, 1 hour after or . . . . + 1 



15 „ +2 



25 „ +3 



19 „* +4 



3 „ +5 



Passiflora cccrulea +8 



Pyrethrum corymbosum (night-bloomer) +10 



Oenothera biennis „ . + 14 



Lychnis vespertina „ . + 15 



Plants whose blossoms open after the commencement of 

 insolation : 



15 species, 1 hour after or . . . . + 1 



6 „ +2 



Passiflora coerulea +5 



Pyrethrum corymbosum (night-bloomer) + 6 



Oenothera biennis „ + 10 



Lychnis vespertina „ +12 



Since the number increases up to three hours after sunrise, and 

 then rapidly decreases, when, at that period, insolation has com- 

 menced, the beginning of insolation may be regarded as the 

 normal period for the cessation of sleep. 



On a consideration of the results of these observations, the 

 following general position may be considered as proved : — Plants 

 require the light of the sun, in order to awake from sleep, either 

 immediately from insolation, or indirectly from diffusion in the 

 atmosphere. In the last respect, the sensitiveness of some plants 

 for light is so great, that their blossoms begin to open the moment 

 the rays of the sun illuminate the higher regions of the atmo- 

 sphere, wbich in summer is the case to a greater or less degree 

 through the whole of the night. A few blossoms therefore expand 

 before sunrise. Since this is connected with no quick accession of 

 intensity of light, but with the transition from the faintest glimmer 

 of twilight to the weakest insolation, the great diurnal periodically 

 returning act of sunrise is not accompanied by any striking effect 

 on the floral world. 



More blossoms do not expand at sunrise than the general and 

 steady accession of intensity of light would lead one to expect. 

 As, however, the intensity of light increases, the number increases 

 which expand, in order to be in readiness to receive the breath of 



