442 
PHYSIOLOGY. 
BOOK II. 
p. m., when it faded, and the smell became very slight. On 
another occasion, when the flower was left on the plant, it 
began to expand at 6 p. m., when the first fragrance was per- 
ceptible in the greenhouse. A quarter of an hour afterwards 
the first puff of odour took place, after a rapid motion of the 
calyx : in rather less than a second quarter of an hour another 
powerful emanation of fragrance took place : by 35 minutes 
past 6 the flower was completely open : at a quarter to 7 the odour 
of the calyx was the strongest, but modified by the petals : 
after this time the emanations of odour took place at the same 
periods as before. Morren considers it probable that these 
exhalations are periodical, because the emission of carbonic 
acid by the same organs takes place also in an intermittent 
manner, and that the emanations of fragrance are a sign of 
the respiration of the flower. 
