304 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1934 



TUFTED GRASSES 



Grasses without rhizomes or stolons grow in tufts, the new shoots 

 arising erect beside the old ones. Such tufts increase in diameter 

 by this gradual accretion at the periphery. If the tufts are very 

 compact the center ultimately dies, since the closely pressed old 

 growth allows no new shoots to appear. There are several grasses 

 on the Great Plains that form such close, regular, circular tufts that 

 they produce " fairy rings." The ring may expand to a diameter 

 of several feet, with a fairly regular border of living plants. For 

 some time the center is so full of old roots and the bases of stems 

 that other plants can get no foothold. Eventually the crowded cen- 

 ter dies out, and after many years the ring begins to break up. One 

 then sees a more or less definite circle of tufts among other grasses 

 which meantime have become established. It is probable that some 

 of these rings are more than 100 years old. 



SEEDS OF PERENNIAL GRASSES 



On the whole, grasses that propagate vegetatively produce a rela- 

 tively small amount of fertile seed. In some species the power to 

 produce viable seed has been almost lost. This is especially true of 

 sugarcane, the only important cultivated perennial grass that is used 

 for food. The large panicles or plumes contain innumerable flowers 

 but few fertile seeds. Until recently the species was thought to have 

 been cultivated so long by vegetative methods that it had lost the 

 power of producing seed. It is now known that occasional seeds are 

 found, and it is these that are used in obtaining new varieties. By 

 planting a whole plume it is found that now and then seedlings appear. 



SEEDS OF ANNUAL GRASSES 



Annuals, on the other hand, necessarily produce an abundance of 

 good seed. This is why primitive man chose annual grasses to culti- 

 vate for food. All our cereals are annuals, improved by long selec- 

 tion. Perennial grasses that are normally poor seed-bearers could 

 probably be improved by breeding and selection. Timothy, a peren- 

 nial meadow grass, produces an abundance of good seed. This is one 

 reason why timothy is a leading commercial grass. 



The life histories of annuals and perennials differ widely. Annuals 

 depend upon wide dissemination of abundant viable seed to maintain 

 their existence. The seed must be deposited in a favorable situation, 

 must retain its viability, sometimes for long periods, and must ger- 

 minate quickly under favorable conditions. Therefore, annuals are 

 found primarily in open ground, cultivated fields, soil thrown up by 

 burrowing animals, and in newly formed soil of any kind. Annuals 



