A SPRIG OF WATER CROWFOOT. 43 



was naturally compelled to split itself up into 

 thinner and narrower segments, each of which 

 grew out in the direction where it could find 

 most stray carbon atoms, and most sunlight, 

 without interference from its neighbours. 

 This, I take it, was the origin of the much- 

 divided lower leaves. 



But a crowfoot could never live perma- 

 nently under water. Seaweeds and their 

 like, which propagate by a kind of spores, may 

 remain below the surface for ever ; but 

 flowering plants for the most part must come 

 up to the open air to blossom. The sea-weeds 

 are in the same position as fish, originally 

 developed in the water and wholly adapted 

 to it, whereas flowering plants are rather 

 analogous to seals and whales, air-breathing 

 creatures, whose ancestors lived on land, and 

 who can themselves manage an aquatic exist- 

 ence only by frequent visits to the surface. 

 So some flowering water-plants actually 

 detach their male blossoms altogether, and 

 let them float loose on the top of the water ; 



