262 



PERIODS OF FLOWERING. 



country ; and by contrasting these periods in different countries, 

 comparisons may be instituted as to the nature of their climate. Thus 

 valuable floral calendars may be constructed. 



Plants are accommodated to the climate in which they grow, 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 neigh- 

 bourhood. From such individuals, by propagation, gardeners are able 

 to produce early-flowering varieties. 



There is a periodicity as to 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. Linnaeus 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 : — 



Plants which expand their flowers in the evening, as some species 

 of Hesperis, Pelargonium, etc., 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 



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