116 



PLANT RELATIONS. 



Fig. 118. Winged fruit of 

 Ailanthus.— After Ker- 



NER. 



reports of "showers of sulphur" have 

 arisen from an especially heavy fall of 

 pollen that has been carried far from 

 some gymnosperm forest. In the case 

 of pines and their near relatives, the 

 pollen spores are assisted in their dis- 

 persal through the air by developing a 

 pair of broad wings from the outer 

 coat of the spore (see Fig. 110). This 

 same method of pollination — that is, 

 carrying the pollen spores by currents 

 of air — is also used by many mono- 

 cotyledons, such as grasses ; and by 

 many dicotyledons, such as our most 

 common forest trees 

 (oak, hickory, chest- 

 nut, etc.). 



78. Dispersal of 

 seeds by air. — Seeds 

 are very rarely light 

 enough to be carried 

 by currents of air 

 without some special 

 adaptation. Wings 

 and plumes of very 

 many and often very 

 beautiful patterns 

 are exceedingly com- 

 mon in connection 

 with seeds or seed- 

 like fruits (see Figs. 

 115, 110, 117, 118, 

 L19). Wings are de- 

 veloped by the fruit 

 of maples and of 



1 Fig. 119. Fruit of basswood (Tiha), showing the 



ash, and by the Seeds peculiar wing formed by a leaf.— After Kerner. 



