Oenothera Gigas. 319 



the main stem in September, by which time the lower 

 fruits are fully grown. The top of the plant still bears 

 a head of flowers and buds. Figures 60 and 61 repre- 

 sent the same two forms at the beginning of the flower- 

 ing period. 



In warm weather the flowers of the Evening Prim- 

 roses open in the evening usually at a rate of 2 or 3 a 

 day, seldom more and sometimes fewer according to the 

 weather. They are pollinated by bumblebees and by 

 Noctuidae {Pliisia gamma, Agrofis segetiim and others) 

 and as a rule wither during the night. The beauty of the 

 flowers has completely disappeared by the following- 

 morning. It is only in cool or even cold weather that 

 the flowers remain open till the following day; but even 

 then they seldom last on into the evening. 



The opening of the flowers has been described by 

 E. RozE.^ The event is a very remarkable one. Early 

 on a beautiful summer evening, when the plants bear 

 nothing but buds and dead flowers, while one may be 

 busied with other operations in the garden, one looks 

 round and suddenly sees every plant in blossom. Half 

 an hour suffices to change the whole aspect of the gar- 

 den. 



The process of opening is in preparation all day. The 

 buds become yellow ; their anthers have completely de- 

 hisced. The tops of the sepals are still joined together 

 to form an entire cap which however becomes split lower 

 down during the course of the day. The petals gradually 

 swell until at last they veritably burst the calyx open, 

 throw the sepals backwards and unfold their free ends. 

 The whole thing happens in a few minutes or seconds. 



* E. RozE. U epanouissement de la Heur de VOenothera suaveolcns 

 Desf. Bull. Soc. bot. France. T. XLII, 8 Nov. 1895, p. 575. 



