OPENING OF THE PASSAGE TO THE INTERIOR OF THE FLOWER. 



215 



contrivances is the closing of the flowers at night. The petals fold inwards and 

 become furled in the same positions as they occupied in the bud. Indeed, one may 

 say that the flower becomes a bud again. When consistent with the advantages 

 accruing from insect-visits, flowers close in the evening and only open again next 

 day when the danger of wetting by dew is past. In a great number of cases this 

 periodic opening occurs at the same hour as that at which the flower-bud originally 

 opened. Many flowers open but once again, others twice, thrice, or four times on 

 successive days — the Meadow Saffron daily for twelve days. As soon as any par- 

 ticular kind of insect begins to swarm, those flowers, whose structure is adapted to 

 visits from the variety of insect in question, open. Similarly, when the insects 

 retire to rest, the flowers close lest the pollen be exposed to needless danger. In 

 other words, the flowers of many plants open and close periodically. 



This remarkable phenomenon has for a long time attracted the attention of 

 Botanists, and Linnjeus devised his so-called Floral Clock on the basis of his long- 

 continued observations at Upsala. In this he grouped together plants according to 

 the hours at which they opened and closed their flowers, and ascertained, for every 

 hour of the day, what species were doing either the one or the other. Not only were 

 simple, isolated flowers laid under contribution for this purpose, but the complex 

 heads (capitula) of Composites also, since these periodic movements are very con- 

 spicuous in them. True, in Composites it is not the petals of a flower which open 

 and shut, but the flowers (florets) of a head; still the cause and efiect are here 

 identical with those in ordinary flowers, and Composites were rightly included in 

 the Floral Clock. If the plants which open and close their flowers periodically be 

 cultivated apart, it is possible to determine the time of day by careful observation 

 in this part of the garden. Formerly, the attempt was often made in Botanic 

 Gardens to construct such a Floral Clock, but never with success, because the plants 

 enumerated by Linneeus do not all flower at the same season. Later, when other 

 fields of Botanical activity came into vogue, it was abandoned as a children's game. 

 Consequently the Floral Clock of Linnaeus has fallen into oblivion, and the younger 

 generation of Botanists hardly knows its name. For my own part, I am inclined 

 to give this Clock some consideration, as it has a bearing on several important 

 questions in the life of plants. To recall it to memory, it is annexed below in the 

 table which follows. It was constructed for Upsala, 60° north lat. 



7 A.M. 



3-5 A.M. 



Tragopogon prate7ue open 



4^5 A.M. 



Cichorium Intyhus „ 



Leowtodon tuberosum „ 



Pioris hieradoides „ 



5 A.M. 



Hemerocallis fulva... 

 Papaver nudicaule . . 

 Sonchus oleraceus.... 



5-6 A.M. 



Crepis alpina open. 



Rhagadiolus edulis „ 



Taraxacum officinale „ 



6 A.M. 



Rieracium wmhellatum.;.... „ 



Hypochceris maculata „ 



6-7 A.M. 



A lysium utriculatum „ 



Crepis rubra „ 



Hieraaitim mtirorum „ 



Hieradum Pilosella „ 



Sonchus arvensis „ 



Anthericum ramosum open. 



Calendula pluvialis „ 



Lactuoa sativa „ 



Leontodon hcLstile „ 



Nymphcea alba „ 



Sonchus Lapponicus „ 



7-8 A.M. 



Mesemhryantliemum barhatum „ 

 Mesemhryanthemum lingui- 

 forme „ 



