DICHOGAMY 



383 



present. Thus, for example, the ash, which has andro- 

 monoecious, gynomonoecious, female, and monocHnous 

 individuals, is also proterogynous. 



Dichogamy is very frequent in hermaphrodite flowers, 

 and in these we find both proterandry, e.g. in Epilohium 

 angusHfolium, Ruta graveolens, the Salvias, and almost all 

 the Composites and Umbelli- 

 feras, and proterogyny, e.g. in 

 Plantago, Helleborus, Thalic- 

 trum, and others. A great many 

 anemophilous species, perhaps 

 the majority, are diclinous and 

 markedly dichogamous. Herma- 

 phrodite wind-pollinated flowers 

 are found in the grasses and in 

 some smaller groups, e.g. the 

 genera Thalictrum,Potamogeton, 

 Plantago, and Rumex (some 

 species of which are diclinous). 

 It is of interest that Plantago, 

 Thalictrum, and Rumex are 

 closely related to entomophilous 

 genera or families, and the infer- 

 ence may be drawn that the 

 anemophilous habit is a recent 

 acquisition (Fig. 55). 



The grasses require special 

 consideration. The predomi- 

 nant condition throughout this great family is herma- 

 phroditism, though some, e.g. the maize, are monoecious, and 

 some show other types of sex distribution. The flowers 

 may be classed as fugacious, as they open, and the stigmas 

 are functional, for a few hours only, often early in the day. 

 The opening— that is, the separation of the pales — takes place 

 by the rapid swelling of the lodicules ; at the same time the 

 filaments undergo very rapid growth, so that the anthers may 

 almost be said to tumble out, emptying their pollen in the 

 air, either at once or very soon after. The feathery stigmas 



A B 



Fig. 55. — Pollination of rib- 

 wort plantain {Plantago lan- 

 ceolata) : A, flower in female 

 stage with petals and stamens 

 still enclosed in the calyx ; 

 B, older flower in male stage. 

 Magnified. (After MuUer.) 



