116 



PLANT RELATIONS. 



Fig. 118. Winged fruit of 

 Ailanthus. — After Kee- 

 ner. 



reports of "showers of sulphur" have 

 arisen from an especially heavy fall of 

 pollen that has heen 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 hy 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. — Many 

 seeds are carried 

 about in various ways 

 by currents of air 

 without any 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, 116, 117, 118, 

 119). Wings are de- 

 veloped by the fruit 

 of maples and of 

 ash, and by the seeds 



Fig. 119. Fruit of basswood (Tilia), showing the 

 peculiar wing formed by a leaf.— After Kernf.k. 



