234 PERIODS OF FLOWERING. 



and flower at certain seasons ; and even when transferred to other 

 climates where the seasons are reversed, they still have a tendency to 

 flower at their accustomed period of the year. Again, in the same 

 climate, some individuals of a species, from a peculiar idiosyncrasy, 

 regularly flower earlier than others. Decandolle mentions a horse- 

 chestnut at Geneva, which flowered always a month before the rest in 

 the neighbourhood. From such individuals, by propagation, gardeners 

 are able to produce early-flowering varieties. 



483. There is a periodicity in the hours of the day at which some 

 species open their flowers. Some expand early, some at mid-day, 

 others in the evening. The flowers of Succory open at 8 A.M., and 

 close at 4 P.M. ; those of Tragopogon porrifolius, or Salsafy, close about 

 mid-day. Linnasus constructed a floral clock or watch, in which the 

 different hours were marked by the expansion of certain flowers. The 

 periods, however, do not seem to be always so regular as he remarked 

 them at Upsal. The following are a few of these horological flowers, 

 with their hours of opening : 



Ipomcea Nil, 3 to 4A.M. 



Tragopogon pratense, 4 ... 5 



Papaver nudicaule 5 



Hypochseris maculata, 6 



Various species of Sonchus and Hieracium, 6 ... 7 



Lactuca sativa, 7 



Specularia Speculum, \ _ _ 



Calendula pluvialis / 



Anagallis arvensis 8 



Nolana prostrata, 8 ... 9 



Calendula arvensis, 9 



Arenaria rubra, 9 ...10 



Mesembryanthemum nodiflorum, 10 ...11 



Ornithogalum umbellatum (Damed'onze heures\ 11 



Various Ficoideous plants 12 



Scilla pomeridiana, 2 P.M. 



Silene noctiflora,.. 5 ... 6 



CEnothera biennis, 6 



Mirabilis Jalapa, 6... 7 



Cereus grandiflorus, 7 ... 8 



484. Plants which expand their flowers in the evening, as some 

 species of Hesperis, Pelargonium, &c., were called by Linnaeus plantce 

 tristes on that account. Several species of Cooperia and of Cereus, also 

 Sceptranthus Drummondii, are nocturnal flowers. Some flowers open 

 and decay in a day, and are called ephemeral, others continue to open and 

 close for several days before withering. The corolla usually begins to 

 fade after fecundation has been effected. Many flowers, or heads of 

 flowers, do not open during cloudy or rainy weather, and have been 

 called meteoric. Composite plants frequently exhibit this phenomenon, 

 and it has been remarked in Anagallis arvensis, which has hence been 



