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SPARTINA PROBLEMS. 



By Prof. F. W. OLIVER, F.R.S. 

 (With 1 Plate and 3 text-figs.) 



From time to time the attention, not merely of botanists, but of whole 

 communities is rivetted, by the sudden appearance of some unfamiliar 

 plant which spreads everywhere in pure stands, often over great areas 

 and to the almost entire exclusion of other forms of vegetation. 



Familiar is the appearance of the fire weed or willow herb (Epilobium 

 angustifolium) where forests have been burnt, charlock and field poppy 

 where ground has been broken by the plough or, as in the devastated 

 areas of France, by high explosive shells 1 . In such cases the character 

 of the ground has been modified so as to favour the production of a 

 new type of vegetation, a vegetation which springs suddenly perhaps 

 from dormant seeds long present in the soil. 



In other cases a like result is produced by the arrival and spread of 

 some exotic plant gifted with great powers of dispersal such as the 

 Russian thistle (Salsola kali) in N. America, and the prickly or pest pear 

 (Opuntia inermis) in Queensland and New South Wales 2 . 



Where fresh water is at once the agent of dispersal and the medium 

 in which the plant grows, very striking effects are apt to be produced — 

 illustrated in recent years by the spread of the water hyacinth (Eich- 

 hornia crassipes) in the navigable waters of N. America (Florida) and 

 Australia 3 , and of Azolla in drains, lagoons and ponds in England and 

 France. More than two generations ago (1842) the newly introduced 

 Canadian waterweed (Elodea canadensis) spread with astonishing rapidity 

 through the river and canal systems of England to the material hindrance 

 of navigation and drainage. In this case propagation was certainly 

 vegetative as Elodea is dioecious and female plants alone have been 

 met with in this country. From Britain, Elodea made its way to the 



1 A. W. Hill, Kew Bull. Misc. Inf., 1917, p. 297. 



2 The Prickly Pear in Australia, Com. of Australia, Inst, of Science and Industry, 

 Bull. No. 12, 1919. 



3 H. J. Webber, The Water Hyacinth, U.S. Dept. of Agric, Division of Botany, Bull. 

 No. 18, 1897. Water Hyacinth in New South Wales, Agr. Gaz. of N.S.W., Dec. 1906. 



