194 



Marvels of the Universe 



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SMn, 



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STORK'S BILL 



FRUITS. 











VVhe. 



the 



seed 



has 



reached 



the r; 



round, the 



con 



traction 



an 





expans 



on 



ol 



ts tail di 



ives 



the seed in 



to 



he soi 



. 





[Bu J. TeUeninro. 

 FEATHER-GRASS SEED. 



central column tjr beak. When the seeds are 

 ripe they move outwards, and are freed by the 

 awns splitting off from the column. And now 

 the true purpose of the awn becomes apparent. 

 It is hj'groscopic — that is, it curls spirally in dry 

 weather and uncoils in damp. The alternation 

 of these movements causes the seed to move 

 along the ground, till it comes to a soft, 

 unoccupied surface, when the awn by its wrig- 

 gling drives the sharp base of the seed into 

 the soil, and the refiexed bristles on the seed 

 prevent it being withdrawn. 



A great number of grass species rely for their 

 dispersal on the hygroscopic properties of the 

 awns and bracts with which thev accoutre their 

 seeds. 



An extreme instance is furnished by the 

 Feather-grass, a native of Russia, and, for- 

 tunately, not naturalized as yet in Great Britain. 

 The seed of this species has a long awn, bent 

 at an angle, exceedingly sensitive to drought 

 and damp, and terminating in a very long 

 feather-like tail which would enable it to fly 

 off some distance from the parent plant be- 

 fore coming to the ground. It is also barbed 

 with bristles like the seed of the Crane's-bill. 

 When the spiral becomes damp it unwinds, 

 with the result that the awn is lengthened, 

 and, as the feathery portion is probably en- 

 tangled in surrounding weeds, lengthening can 

 onl}' take place in a downward direction ; so 

 the seed is driven into the ground. At the next 

 dry period, when the shaft again becomes a 

 spiral, the seed cannot be dragged out of the 

 soil because the barbs prevent it. At each 

 atmospheric change the seed will get driven 

 a little further in until it is deep enough for 

 growth to begin. When this awn attaches 

 itself to the wool of a sheep by winding and 

 unwinding itself, it drives the hard, sharp point 

 of the seed into the animal's skin, whence the 

 barb-like bristles prevent it being withdrawn, 

 thereby' causing intense irritation and, in some 

 cases, actually killing the sheep. It is a re- 

 markable fact that in three other parts of 

 the world, widely separated, namely. North 

 America, New Caledonia and Queensland, there 

 exist as many different species of grass which, 

 by similar means, exact upon sheep the same 



