72 SEEDS WAFTED BY WATER. [ch. hi. 



flexible, and wrap round the wool of any animal with 

 which they may come in contact, so that they form a 

 double means of dispersion. 



The Marygold {Calendula), so often grown in our 

 gardens, is remarkable for having three forms. It is 

 a Composite, and there are numerous florets, each 

 producing an achene, in one head. The outer rows are 

 much curved, and thus attach themselves to any 

 passing animal ; then follow one or two series the 

 side margins of which are drawn out, so that they are 

 much lightened and, as it were, hollow. These are 

 easily carried by even a slight wind. The inner ones 

 are curled, and closely resemble small green or brown 

 caterpillars. They are probably seized by birds and 

 carried some little way before the imposition is 

 detected. Thus this interesting species has devised 

 three distinct methods of providing for the diff"usion 

 of its seeds. 



In other cases seeds are wafted by water. Of this 

 the Cocoa-nut is one of the most striking examples. 

 The seeds retain their vitality for a considerable time, 

 and the loose texture of the husk protects them and 

 makes tBem float. Every one knows that the Cocoa- 

 nut is one of the first plants to make its appearance 

 on coral islands, and it is, I believe, the only palm 

 which is common to both hemispheres. 



The seeds of the common Duckweeds {Lemna) 

 sink to the bottom of the water in autumn, and re- 

 main there throughout the winter ; but in the spring 

 they rise up to the surface again and begin to grow. 



