Anthesis • 129 



darkness, anthesis occurs with circadian periodicity for several 

 days, but only in those buds that had developed largely under 

 normal day-night changes. Buds that develop from a young stage 

 in total darkness are considerably delayed in anthesis, and finally 

 open more or less at random. In addition, light must be given 

 directly to the buds to reset or disturb the periodicity of anthesis— 

 lighting schedules given to the leaves are ineffective. 



Other evening-blooming plants have been studied recently. 

 Anthesis of the giant tropical water lily Victoria regia normally 

 occurs soon after sunset (6 p.m.). It can be moved up as early as 

 4 p.m. by darkening the buds with black paper for 30 minutes, but 

 darkening earlier than this hour has no effect; therefore some endog- 

 enous component, perhaps set by preceding illumination schedules, 

 is involved in the sensitivity to darkness. Illumination during the 

 night delays the opening of buds during the next days, but 

 eventually they open even in continuous light (Gessner, 1960). 

 The opening and odor production of the night-blooming jasmine, 

 Cestrum nocturnum (an LSDP discussed earlier), show a circadian 

 rhythm in constant light or darkness. In constant light, the period 

 length is roughly 27 hours at 17° C; higher temperatures reduce 

 it by several hours, and lower temperatures increase it (Overland, 

 1960). 



Daily timing of anthesis is probably regulated in the ways 

 indicated above, but much less is known about the control of 

 anthesis in those indirect-flowering plants whose fully developed 

 buds may remain dormant for a considerable period and then open 

 in the course of a few days. Among temperate-zone plants this is 

 usually the result of the breaking of dormancy by long cold exposure 

 followed by periods of favorable temperatures for growth; as such, 

 it resembles the breaking of other forms of dormancy by low 

 temperature (see Chouard, 1960). Though this does not explain it, 

 there is no need for further consideration as a separate topic here. 

 Certain tropical plants, however, show the same extended bud 

 dormancy, and the same explanation cannot hold for these. 



One of the few examples studied with any thoroughness is 

 coffee, Coffea arabica. This is an SDP as far as flower initiation is 

 concerned (Chapter Seven), but bud dormancy and anthesis appear 

 to be controlled by moisture conditions. Under relatively dry con- 

 ditions, rapid and uniform anthesis can be brought on by heavy 



