SECT. I. EXCITABILITY. 445 



in the case of compound flowers, as in that of the 

 Dandelion and Havvkweed. But the most singular 

 case of this kind is perhaps that of the Lotus of the 

 Euphrates as described by Theophrastus, which he 

 represents as rearing and expanding its blossom by 

 day, closing and sinking down beneath the surface 

 of the water by night, so as be beyond the grasp of 

 the hand, and again rising up in the morning to 

 present its expanded blossom to the sun.* The 

 same phenomenon is related also by Pliny.-f~ 



But although many plants open their flowers in 

 the morning and shut them again in the evening, 

 yet all flowers do not open and shut at the same 

 time. Plants of the same species are, however, 

 pretty regular to an hour, other circumstances being 

 the same ; and hence the daily opening and shutting 

 of the flower has been denominated by botanists 

 The Horologium Flora. Flowers requiring but a Horolo- 

 slight application of stimulus open early in the florae, 

 morning, while others requiring more open some- 

 what later. Some do not open till noon, and some, 

 whose extreme delicacy cannot bear the action of 

 light at all, open only at night, such as the Cactus 

 grandiflora, or Night-blowing Cereus. 



But it seems somewhat doubtful whether or not Islightthe 



f, . , sole agent? 



light is the sole agent in the present case ; tor it has 

 been observed that equatorial flowers open always 

 at the same hour, and that tropical flowers change 

 their hour of opening according to the length of 



, re. A. ] Lib. xiii. 18. 



