SEX DISTRIBUTION 331 



separation of the sexes is frequently incomplete, and a few 

 male flowers may be found on the female plant, and vice 

 versa, e.g. in Mercurialis annua. 



More complex are the relations in those species with 

 hermaphrodite as well as unisexual flowers. We must 

 distinguish : — 'A. Species all individuals of which have the 

 same kinds of flower : {a) all individuals have both herma- 

 phrodite and female flowers, are^j'«owo«ceaoi^^,e.^.Parietaria; 

 (Z>) all individuals have hermaphrodite and male flowers, are 

 andromonoecious, e.g. iEsculus ; (c) all individuals have 

 hermaphrodite, male, and female flowers, are trimonoecious , 

 e.g. Poterium Sangidsorba. B, Species in which different 

 individuals have different types of flowers : {a) gyjiodioecioiis 

 species, of which some individuals have hermaphrodite 

 and others female flowers, e.g. many Labiata; ; {b) andro- 

 dioecious species, of which some individuals have herma- 

 phrodite and others male flowers, e.g. Caltha palustris ; 

 (c) triceciom species, of which some individuals have herma- 

 phrodite, others male, and yet others female flowers, 

 e.g. Empetrum nigrum. Polygamous is a general term applied 

 to species with three types of flowers. 



This does not exhaust the possible or actual combinations. 

 We may give as an example of further types, Silene inflata 

 with male, andromonoecious, female, gynomoncecious, and 

 individuals with hermaphrodite flowers. Moreover these 

 types must be regarded to a certain extent as ideal, for 

 distribution is rarely quite clean cut. Thus irregularities 

 occur even in monoclinous and simply monoecious and 

 dioecious species, where the constancy is greatest. Thus 

 Stout (19 1 9) has shown that in Plantago lanceolata, the 

 flowers of which are normally hermaphrodite, individuals 

 may be found showing every gradation between this con- 

 dition and complete suppression of pollen production. 

 Davey and Gibson(i9i7) have studiedMyrica Gale, a species 

 usually described as dioecious, and they find individuals, 

 {a) with male and female catkins, {b) with catkins bearing 

 male and female flowers, (c) with hermaphrodite flowers. 

 The willows are very regularly dioecious, but Schaffner 



