SEED SOWING 207 



the openings, in response to the changes of 

 weather. 



AIR GLIDERS 



No one knows how long ago ambitious navigators 

 learned to hitch their frail barques to the sea breeze 

 to carry their cargoes, but it is certain that in very 

 early ages the pines and other tall trees learned to 

 take advantage of the wind in like manner, as a 

 means of spreading their seeds. So each seed was 

 built like a biplane, or air glider, 

 as we have seen in a previous 

 chapter. A seed of the pine, with 

 its small sail, was represented in 

 our sketch on page 166. That of the maple, much 

 larger and very familiar, is shown here. We have 

 all seen them floating down from maple-trees, and 

 twirling as they slowly fell. The lightest breeze 

 can carry them a long way ere they reach the 

 ground. We find similar seed-sowing practised by 

 the elm, ash, birch, hornbeam, linden and catalpa. 



AIRSHIP SEEDS 



But these gliders are comparatively heavy seeds. 

 There are many others far lighter for their dis- 



