330 THE BIOLOGY OF FLOWERING PLANTS 



But as the male gametophyte is always derived from the 

 spore produced by the stamen it is not unnatural to extend 

 the term male to the stamen ; and so for the carpel. Strictly 

 speaking the sexes in the flowering plants are always 

 separated and occur on two different individuals. When 

 we talk, however, of sex distribution in the flowering plants 

 we mean the distribution of the mega- and micro-sporophylls ; 

 we use the word sex in the looser sense which carries over 

 the sexual character to the spores, to the organs which 

 produce them, and finally to the sporophytes themselves. 



The distribution of sex in this sense in the flowering 

 plants is very complex and varied, and it is not possible 

 here to do more than outUne the various conditions which 

 occur. We must in the first place distinguish between 

 flowers which are hermaphrodite with both stamens and 

 carpels, and those which are unisexual and have only the 

 one or the other. In the angiosperms the hermaphrodite 

 flower is the commonest type, and it probably represents 

 the primary condition in this group. Unisexual flowers have 

 arisen by the suppression of one or the other essential organ, 

 as is indicated by the numerous cases in which the suppres- 

 sion is normally or occasionally incomplete. Suppression 

 may go so far that both stamens and carpels disappear and a 

 flower results which has attractive functions only, as in the 

 marginal flowers of the inflorescences of many Umbelliferas 

 and Compositas. In the gymnosperms unisexual flowers 

 (cones) are the rule, and this condition is primary. Only in 

 Welwitschia is a rudimentary ovule present in the male 

 flower, though hermaphrodite cones are known as abnor- 

 malities in some conifers. 



A species or individual with hermaphrodite flowers is 

 termed monoclifious, in contrast with a species having male 

 and female flowers, which is diclinous. In the simplest cases 

 all the flowers are either hermaphrodite or unisexual. 

 Diclinous species with male and female flowers on the same 

 individual are monoecious, e.g. the hazel ; if the male and 

 female flowers occur on different individuals the species is 

 dioecious f e.g. the willows. In dicecious species the 



