PERIODICAL OPENING AND CLOSING OF FLOWERS. 7 



no alteration of phase, whereas the change is the most striking 

 exactly at those periods of the day when the angle of the sun's 

 altitude changes most rapidly. 



The duration of expansion is clearly merely the complement of 

 that of remaining closed within the twenty-four hours. The time 

 of the day, however, at which the greatest expansion takes place 

 deserves notice, for the vital powers are there exhibited in the 

 greatest action. 



In general, the number of species whose blossoms attain the 

 maximum of their phase increases from sunrise to midday, and 

 then decreases till sunset. None of the day-bloomers is open till 

 7 a.m., or later than 5 p.m. A similar law seems to hold good 

 with the night-bloomers, which generally seem to open their cup 

 fully towards midnight, while at mid-day they are completely 

 closed. Now if these results are arranged as in Table A. we 

 have, — 



TABLE B. 



