68 



POLLINATION 



into the air to a distance of several inches. This gives it a good start 

 on its journey. The birches, on the other hand, are monoecious, with 

 both kinds of flowers in catkins (Fig. 25). The oaks, hickories, 

 walnuts and hazels are also monoecious but have only their staminate 

 flowers in catkins. The pistillate flowers are either solitary or only 

 a few in a cluster. 



Fig. 25.— Yellow birch (Betula luiea). Wind pollinated. Staminate catkins 

 above, pistillate below. (Photograph by John H. Lovell.) 



Among other trees that are wind-]X)llinated are the beeches, elms 

 and ashes. In the beech the pistillate flowers are in pairs while the 

 staminate flowers are clustered in globose heads, 2 or 3 cm. in diam- 

 eter, which hang downward at the ends of long slender peduncles. 

 The flowers of the elm are Iwrne in small loose clusters. They are 

 mostly perfect and close pollination is largely prevented by pro- 

 togyny. Some species of ash are dioecious while others are mono- 



