COLTSFOOT FLOWERS. 



shaped bases and their obtrusive angles ; 

 while the under side is thickly covered 

 throughout with a cottony wool, loose, white, 

 and abundant. They are big, because they 

 overtop the other leaves about, and so gain 

 free access to the air and sunshine. They 

 have elbow-room to spread in. Their busi- 

 ness (like that of all leaves) is to catch and 

 eat carbonic acid, which the sunlight assimi- 

 lates for them. For this reason they are 

 green above, with a transparent skin, which 

 skin forms a water-layer for absorbing the 

 gas and conducting it to the living green 

 tissue beneath, where it is duly digested 

 and assimilated. But why the cotton below ? 

 Well, the upper and under surfaces of leaves 

 perform in nature quite different functions. 

 The upper side, which is thick and firm, 

 eats carbonic acid and receives the incident 

 sunlight to digest it ; but the under side, 

 which is looser and spongier, gives off 

 vapour of water transpires, as we say by 

 innumerable little mouths, which are its 

 in 



