PERIODICAL OPENING AND CLOSING OF FLOWERS. 13 



sion increasing, blossoms are perfectly closed when the temperature 

 attains certain limits. At what temperature this takes place 

 appears from the following table : — 



Temperature at which all motion of the corolla ceases : 



74'75 three species. 

 83-75 three „ 

 88-25 five 

 92 - 75 four „ 

 97-25 seven „ 

 101-75 Commelina ccelestis. 



These then are flowers which cannot bear a temperature of 

 7475, while others endure up to 97 - 25° and above. It is worthy of 

 remark, that the greater number are collected at 97 - 25, the 

 absolute limit of the temperature of the air in the latitude of 

 Prag, beyond which limit examples are very rare. 



The importance of the part which is played by the temperature 

 of the air is very evident from these facts : except it reaches a 

 certain height, blossoms do not begin to open ; they are not fully 

 expanded, but only proportionally till it attains a definite degree ; 

 when it exceeds this, some blossoms close, while others probably 

 are at their greatest phase, till the temperature sinks below a 

 certain limit. The daily course of change must thence be infi- 

 nitely modified. If the temperature in the course of the day does 

 not at any hour reach that degree at which the motion of the 

 corolla begins, the more or less closed blossoms will exhibit the 

 same form through the whole day for want of sensibility, and 

 probably, also, stand still as regards their evolution or even their 

 vital functions. The opposite case will arise if the temperature 

 keep continually at that height which is requisite for the full 

 expansion of the blossoms. If the range of temperature remain 

 within these bounds, that of change will not reach that limit. 



In the following table the plants are arranged according to the 

 alteration of phase which takes place on an increase or decrease of 

 22-50 of temperature (18 Reaumur); we have here the first 

 approximation to the co-efficient for the reduction of the phase for 

 a specific and equal temperature, and the means of judging 

 whether the daily range of expansion depends alone on the range 

 of temperature or on other circumstances. The co-efficient is 

 valid within the degrees of temperature to which the motion of 

 the petals is confined, and is positive between (t . . . T) where t is 

 the temperature at which the flower begins to expand, T the 

 temperature at which the maximum expansion takes place ; and 



