14 PERIODICAL OPENING AND CLOSING OF FLOWERS. 



negative between (T . . . f) where t' is the temperature at which 

 all motion ceases. 



This shews clearly the immense influence of temperature. In 

 a few plants only the petals approach the horizon, on an increase 

 of 22 - 5°, less than 30°, or what is the same thing, diverge from 

 each other when opposed less than 60°. In most cases the 

 increase of divergence extends from 80° — 170°, in individual cases 

 as much as 240° and in Tigridia pavonia above 820°. 



Even those blossoms, whose phase is altered together with the 

 temperature, in the same sense, change their range into the 

 opposite when the temperature exceeds certain limits. This is the 

 case with those plants which form the transition from day-bloomers 

 to night-bloomers. Though it cannot be denied, taking these 

 observations into consideration, that temperature is far the most 

 important agent as regards the magnitude of the changes which 

 take place in the phases of flowers, such alteration cannot be 

 sufficiently explained from the diurnal range of temperature 

 alone, but other meteoric agents probably are at work. The 

 answer to this question supposes the co-efficients of temperature 

 and its limits to be more accurately and fully determined than is 

 at present the case. 



3. Insolation. — The inquiry with respect to the influence of 

 insolation, or exposure to the direct rays of the sun, has the most 

 intimate connexion with what has been said, for at that time of the 

 year when plants expand their blossoms, insolation is the most pro- 

 ductive source of high temperature. Beyond doubt, however, it 

 exercises not only this but also an immediate influence on the 

 expansion of flowers, in consequence of their susceptibility for the 



