GRASSES — HITCHCOCK 301 



are self-fertilized cleistogamous spikelets of a single large floret 

 with larger grains, quite different from those of the terminal panicle. 

 At maturity the stem, with its sheath and enclosed grain, disjoints 

 at the node below and can be blown about by the wind. The num- 

 ber of species known to produce cleistogamous spikelets in the lower 

 sheaths is constantly increasing as attention is given to the subject.^ 



VEGETATIVE PROPAGATION 



Propagation of grasses may be by seed or by various vegetative 

 methods. Annuals depend absolutely on their seeds for the con- 

 tinuation of the species. Perennials are less dependent on seeds 

 since the individual may survive indefinitely. In a general way 

 the perennial grasses may be divided into two groups, the tufted 

 kinds that form crowns, and those that spread by means of rhizomes 

 or stolons. 



Khizomes or rootstocks are creeping underground stems, from the 

 nodes of which upright shoots are produced thus establishing new 

 plants w^hich in turn form more rhizomes. Such plants are likely 

 to be gregarious. They are found mostly in loamy, sandy, or muddy 

 soil where the rhizomes meet with little resistance. In marshes 

 they are constantly extending on the water side and retreating on the 

 land side. The thick growth of the stems allows the deposit of 

 additional material, thus building up soil from the bottom. Finally, 

 the conditions on the land side are less favorable to the growth of 

 the species, and it fails to withstand the competition of other species. 

 Meantime the marsh is being converted into dry land. 



SAND-BINDERS 



Other rhizomatous species are at home on sand dunes. The best 

 known of these dune grasses is the beachgrass {Amnnophila arenaria) 

 of Europe, where it is planted extensively to hold drifting sand 

 along the coast. The region now occupied by Golden Gate Park, 

 San Francisco, was once a sterile waste of sand such as is seen along 

 the coast to the south. Beachgrass was imported and set out to hold 

 the sand. After the sand had been fixed by the grass, trees were 

 planted, the soil was enriched, and there has gradually emerged 

 the beautiful park we see there now. 



Along the sandy coasts of Europe beachgrass is planted to form 

 the great barrier dunes that protect the land behind. Trees are 

 grown in the lee of the dune, but these cannot withstand the severe 

 conditions of the dune on the side toward the sea. The barrier dunes 



^ Those interested may consult an article entitled "Axillary Cleistogenes in some 

 American grasses", by Agnes Chase, Amer. Journ. Bot., vol. 5, p. 254, 1918. 



