The Book of Grasses 



out into deserted country roads, and spreading far and wide by 

 means as interesting as ever the more noted flowering plants 



employ. 



Bur-grass, with its thorny seed-burs, catches on passing ob- 

 jects and thus secures free portage to new fields; Terrell-grass by 

 thick, corky scales floats its seed upon the streams near which it 

 grows; Beach Grass defies the sand to bury it and is found at the 

 tops of the highest sand-dunes, with whose rise it has kept pace, 

 the long roots of the grass penetrating to the base of the dune; and 

 Couch-grass, sending sharp-pointed rootstocks rapidly through 

 the soil, is a veritable "land-grabber." 



Where the purslane and poppy produce a multitude of seeds 

 from every flower, each blossom of the grass ripens but one, yet 

 so richly stored is this with nutriment, and frequently so well 

 protected against germination under unfavourable conditions, that 

 the one seed may be worth many of those less perfectly equipped, 

 since, in the process of evolution, diminution in the number of 

 seeds is accompanied by an increase in the effectiveness of those 

 that remain. 



The twisted awns of certain grasses — e. g.. Sweet Vernal- 

 grass and Wild Oat — show one of the most interesting mechan- 

 isms seen in the vegetable world. These awns, or bristle-like 

 appendages of the grass flower, are extremely sensitive to atmos- 

 pheric changes, and by their peculiar structure aid in burying the 

 seed beneath the surface of the soil. In Sweet Vernal-grass the 

 scale, to which the ripened seed adheres, bears a brown awn, bent 

 and twisted near its middle, and beset with minute, upward- 

 pointing hairs on its basal part. Such awns are strongly hygro- 

 scopic and during cold or dry weather remain tightly twisted, thus 

 holding the seed where it chances to be. Under the influence of 

 moisture the awn untwists and by its rotation drives the fallen 

 seed slowly but surely beneath the soil. Although dry weather 

 may follow, causing the awn to become twisted again, the upward- 

 pointing hairs catch on particles of earth or grass and, holding the 

 seed down, prevent it from being drawn up. Thus it lies ready 

 for the next shower when the awn pushes the seed farther into the 

 earth. This peculiarity of structure is easily observed without the 

 aid of the microscope. If a few of the ripened seeds be laid upon 

 the moistened palm of the hand they will immediately begin to 

 move, as if alive, and the rotating of the awn may be plainly seen. 



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