384 THE BIOLOGY OF FLOWERING PLANTS 



likewise protrude, standing out above the pendent stamens. 

 Most grasses follow this scheme of opening ; in some 

 genera, e.g. Phleum, Anthoxanthum, Nardus, the pales 

 do not open, and the stamens and stigmas push forcibly 

 between their edges. Some grasses are described as 

 proterandrous, some as proterogynous, and many as homo- 

 gamous. It is obvious that, even where dichogamy obtains, 

 it can be little marked when the open stage of the flower 

 lasts only a few minutes or hours. The stigmas may be 

 exposed alone for a few minutes, or the stamens may have 

 shed their pollen shortly before the protrusion of the 

 stigmas, but the separation can never be very great. Many 



Fig. 56. — Flowers of oat ; left with stigmas exposed, right with stamens 

 dehiscing. X 2. (After Kerner.) 



grasses are habitually self-pollinated before the flower opens. 

 This is notably the case in the oat, wheat, barley, and rice ; 

 to what extent it is a property of cultivated races does 

 not seem to be known (Fig. 56). 



In wind-pollinated plants, then, dicliny and dichogamy 

 predominate. With pollen scattered broadcast sex 

 separation is the only available method of securing cross- 

 pollination. In the grasses, however, we have a great and 

 very successful family in which the flowers are herma- 

 phrodite ; where dichogamy does occur it is so little accen- 

 tuated that its efTectiveness may be doubted in absence of 

 experimental proof to the contrary. 



