226 DIAL OF FLOWERS. 



to endure the light of the sun and to perform the 

 functions for which they are designed. It is not 

 till they are capable of fulfiUi?!^ these functions that 

 the flower unfolds itself; but it again closes at such 

 times when external influences might be injurious to 

 the delicate organs of fructification. Many flowers 

 can bear only the refreshing morning air and the 

 first rays of the sun, but remain shut all the rest of 

 the day. This may be particularly observed in 

 the diflerent species of Convolvulus, Ipomsea, and 

 Goat's Beard. We find these in general open only 

 till about eleven o'clock. In like manner the Mal- 

 lows and the Mesembryanthemums unfold their 

 flowers about noon, and precisely at that time, in 

 serene weather, open the singularly formed Drosera, 

 and the common Purslain, which shut again in an 

 hour. Others unfold themselves only in the evening 

 and continue open all night, probably because their 

 delicate organs would be injured by the sun. The 

 CEnotheras, the Gauras, and the different species of 

 the Mirabilis, furnish examples of this kind. Thus 

 too the Cactus opuntia opens its magnificent blos- 

 soms at night only, and towards morning shuts them 

 up for ever. The flowers of many plants of the 

 nineteenth class are observed to hang their heads 

 during night — the Camellia, for example — by which 

 means the rain, or dew, which might injure the 

 tender organs of fructification, can run off the more 



