19 



len grains is such that it is easily carried by the wind. It 

 consists of three cells, one of which only is fertile. The 

 others serve to buoy the pollen and therefore make it of easy 

 transport. The pistillate flowers are colored red, and have a 

 large receptive surface. 



Pollen of conifers has been carried for more than a hun- 

 dred miles. The so-called "showers of sulphur" on ponds 

 consist of pollen grains which were suspended in the air 

 and brought down during a shower of rain. 



Alder '^^^ alder, which is a common plant in Eastern States 



and Northeastern Iowa, bears its stamine flowers in 



long festoons. The pistillate catkins are more or less erect. 



Fig. 10. 

 ner von Marilaun.) 



FIG. 10. 

 1-2 Bhodiidendrnn hirsutum, i Bpilobium angustifoHum. (After Ker- 



Usually self-pollination is not prevented in the cultivated 

 European species, nor in some of our wild species. 

 John H. Lovell states the Alnus incana is partially dioecious. 

 Honey bees occasionally visit the stamine flowers for pollen. 



