DISPERSION AND GERMINATION OF SEEDS. 221 



travel for miles until a shower of rain or a humid atmosphere 

 causes the tuft to collapse, when the pericarp falls to the 

 ground. In some instances, as in the thistle, this down pro- 

 jects directly from the surface of the pericarp like the feathers 

 of a shuttle-cock; in the dandelion and goatsbeard it is sup- 

 ported upon a stalk which elevates it above the seed. In the 

 last plant each fine hair of the tuft is itself a feather, forming 

 altogether one of the most elegant and perfect objects. 



In other species the pericarps are furnished with hooked 

 hairs, which cover their entire surface, as in galium and bur- 

 dock, by means of which they cling to the bodies of men and 

 animals, and are thus scattered far and wide. In autumn it is 

 impossible to traverse the woods marshes without having 

 such pericarps forced upon our attention. The achenia of 

 Bidens bipinnata, or the Spanish needles, are especially trou- 

 blesome. The achenia of this plant are surmounted with three 

 or four persistent awns, which are downwardly barbed, and by 

 means of which they very readily adhere to the dress of the 

 traveller. How little are persons aware when they brush off 

 these troublesome intruders, in some distant locality to which 

 they have unwillingly carried them, that they are fulfilling the 

 grand and secret purposes of nature ! 



Occasionally, as in the Asclepias or milkweed, and the Epi- 

 lobium or willow-herb, the seeds themselves are furnished 

 with the coma or tufts of hairs, by means of which, on the 

 dehiscence of the pericarp, they are lifted by the wind out of 

 its cavity and carried away sometimes to a great distance from 

 the parent plant. 



Birds, too, are important agents in the diffusion of seeds. 

 It is well known that the seeds of numerous berries and small 

 fruits will grow, though they have passed through the bodies 



