8 THE AMERICAN BOTANIST. 



and if pollen from a flower of a different order happens to 

 fall on the stigma it has no effect. But in plants of the 

 same genus, or in varieties of the same .species it is often 

 eas3' to make crosses, and the closer the plants are related 

 the easier it is. 



Still more striking instances of the necessity for cross- 

 pollenation are found in plants that bear their stamens 

 and pistils in different flowers. In such cases it is abso- 

 luteh' necessary that pollen be brought from some other 

 flower. A corn-field, at this season, is an excellent place 

 to study this subject. First there is the corn whose stam- 

 inate flow^ers (the "tassel") are borne high above the 

 pistillate ones (the ear) whose long styles are well known 

 by the name of corn "silk." Down on the ground sprawl 

 the pumpkin vines whose pistillate flowers are eas3^ to 

 distinguish from the staminate from the fact that thcA- 

 each have a tiny pumpkin l)elow them. The whole gourd 

 famih^ has this peculiarity, and one may see it in the cu- 

 cumber, musk melon, and squash. The corn and pumpkin 

 also stand for two distinct methods of pollenation, for 

 while the corn trusts its pollen to the wind, the pumpkin 

 relies upon insects, mostly honey-bees in our latitude. 



Other well known plants with flowers in which the 

 sexes are separate are the alders, oaks, birches, chestnuts, 

 sweet-fern, begonias and some of the nettles. There are 

 still other species with stamens and pistils on different 

 plants, and of these the willows, poplars, meadow rue 

 {Thnlictrum), hop and hemp are familiar instances. In 

 such cases w^e have entire plants whose only use to the 

 species is to furnish i)ollen for others, since the^' can never 

 set seed themselves. 



Under these circumstances it is very evident tliat some 

 agency is needed for transferring the pollen from one 

 flower to another. The wind serves the pines, aspens, 

 grasses, sedges, oaks and others. Most wind pollenated 

 plants are remarkable for producing immense quantities 

 of pollen, for when this is sown on the wind there must 

 be an abundance if no stigma is to be missed. The stig- 



