DISPERSION. 297 



coltsfoot afford an example of a structure, common 

 in the order, where the seed is surmounted by a tuft 

 of silken hairs armed, at regular intervals, with a 

 series of denticles or spines, only visible with a good 

 magnifier. We have a contrast to this in the curious 

 fruit of the blue-bottle (Centaurea cyanea) which has 

 a small tuft of asbestine spines at the base, and a large 

 but short tuft of rigid stout lanceolate spines on the 

 top, the edges of each of them indented with close 

 and sharp serratures like a saw. This tuft cannot 

 float the seed in the air, but it will obviously direct 

 and hasten its descent into the soil, and it will be 

 remarked that the forward direction of the spines 

 must be opposed to every influence to cast them up 

 again, after having been buried under the surface." 1 



The stalks of the down in the dandelion contract 

 closely together in moist and wet weather — a beau- 

 tiful provision to secure its dispersion only in a dry 

 day, when it is driven off by every zephyr, and not 

 unoften by the schoolboy, who thus endeavours to 

 resolve his doubts as to the hour : — 



Dandelion, with globe of down, 

 The school-boy's clock in every town, 

 Which the truant puffs amain 

 To conjure lost hours back again. 



The dispersion of seeds by means of a coronet of 



delicate hairs is not confined to composite plants. 



1 Johnston's " Botany of the Eastern Borders," p. 126. 



