130 • A Miscellany 



rains or irrigation— even by wetting the buds themselves. This 

 suggests that the seasonal dormancy is simply due to a water deficit 

 and disappears when water is supplied. But the situation is probably 

 not this simple. Alvim (1960), working in a dry area where the 

 water conditions on a plantation were completely controllable by 

 irrigation, found that coffee plants irrigated at weekly intervals 

 failed to reach anthesis over a long period of time. Others, allowed 

 to remain dry for a shorter length of time and then given one good 

 irrigation, responded with heavy anthesis within two weeks. It 

 thus seems likely that a period of water deficit is required to break 

 bud dormancy in this plant, so that anthesis is brought about by 

 a thorough wetting after a dry period. Alvim suggests that this may 

 be a major form of seasonal control of anthesis in tropical plants, 

 a control in some respects ecologically analogous to that exerted in 

 temperate-zone plants by low temperatures followed by warming. 



THE SEX EXPRESSION OF FLOWERS 



Flower primordia in a given species do not always give rise to 

 identical structures, even if development is perfectly normal. 

 Although probably the great majority of plants produce one kind 

 of flower, with both functional stamens and functional pistils— a 

 hermaphrodite or monoclinous flower— some do not. Unisexual (or 

 diclinous) flowers, either staminate or pistillate, occur in many 

 species. There are also intermediate conditions of various kinds. 

 If staminate and pistillate flowers are borne on the same individual, 

 the plant is said to be monoecious; if on separate individuals, 

 dioecious. Until relatively recently, these phenomena of "sex ex- 

 pression" have been studied largely from the morphological and 

 genetic points of view, but they are frequently modifiable by 

 environmental and chemical means as well. For a recent review of 

 the genetic factors, see Westergaard (1958). A comprehensive 

 review by Heslop-Harrison (1957) on the experimental modifica- 

 tion of sex expression is the basis lor the general statements not 

 otherwise documented in the discussion below. There is some 

 controversy over the evolutionary origins of sex expression in plants 

 and even over the proper terms in which to discuss it (see the 

 references cited and also Heslop-Harrison, 1958). 



Consideration of the effects of light and temperature on sex 



