THE DISPERSION OF SEEDS AND SPORES. 79 



fruit is elevated as a person's body is raised 

 when he stands on tiptoe. By the spreading of the 

 pappus the fruits literally lift themselves out of the 

 involucre as if on stilts, and from the ripe capitulum 

 the thistle-downs appear to issue like foam. From 

 the capsules of the willow, poplar, and cotton-plant, 

 the seeds also lift themselves out by the spreading- 

 of their hairs. To see the thistle-seed thus raised 

 and poised on the edge of the capitulum, shaking 

 out its silken fringes in the dry autumnal air, reminds 

 one of a bird pluming its feathers preparatory to 

 flight. When at last its snowy pinions are fully 

 expanded, and it soars away on the breeze, we need 

 only follow it a little to see that the adaptation 

 does not end here. Should the fruit collide with 

 a branch or other object the shock is generally 

 sufficient to detach the solid seed from its pappus. 

 The plumes, having served their purpose, are dis- 

 carded, and the seed, freed from encumbrance, falls 

 to the soil. The readiness with which the smooth 

 solid portion of the fruit becomes detached is an 

 important provision enabling it readily to penetrate 

 matted vegetation and reach the soil. This, no doubt, 

 arises from the continued desiccation of the pappus. 

 A very curious special provision, favouring the 

 departure of the seeds, occurs in the willow-herb 

 (Epilobium). The narrow elongated capsule splits 

 into four linear valves which separate from the 

 central axis, but the seeds, instead of falling out, 

 remain suspended in four vertical rows between the 

 valves. This cresset-like arrangement might be said 

 to resemble roughly four vertical ladders set in a 

 square. On the middle of each rung of the ladders 

 a seed is perched, the rungs themselves being formed 

 by the hairs of the arillode with which each seed is 

 furnished. The tuft of hairs on every seed is parted 

 in the middle, one half being attached to one valve 

 and the other half to the next. The way the seeds 

 are superimposed on one another gives to each of 

 the four vertical series a herring-bone appearance. 



