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BOTANICAL GAZETTE [February 



No. 5.— Duxes, Golden Gate Park, San Francisco, Cal. 



Per cent. Per cent. 



Insoluble matter 88.27 Alumina 108 



Soluble silica 4.42 Water and organic matter 2.15 



Lime 1 . 94 Nitrogen .05 



Potasb 0.17 Other constitutents 1.80 



Phosphoric acid (soluble) 0.08 Total 100.01 



Peroxid of iron o . 05 



These analyses show what a small amount of plant food is available 

 in the dunes in comparison with that in ordinary agricultural soil, 

 where the insoluble substances do not comprise more than 70 per 

 cent, of the total volume. And it must be remarked that the analyses 

 here given represent soil from places more or less covered with vegeta- 

 tion, where the organic constituents are better preserved from decom- 

 position and from being washed out by water than on open sand. 

 They therefore show a higher percentage of humus and soluble 

 material than the barren quartz unprotected from the influence of 

 sun, air, and water. Where sand has recently been deposited after 

 having been exposed for some time to sea water it is naturally very 

 deficient in plant food, and it has therefore to be considerably changed 

 before it is able to sustain a vegetation covering. 



The amount of lime contained in the dunes varies to a great extent. 

 On tropical coasts it is generally very large, especially where the sand 

 i formed by disintegration of coral rocks. On such shores carbonate 

 of lime is dissolved by the rain water and the sand is at a low depth 

 under the surface consolidated into limestone. A similar process o 

 calcification can be observed also on many coasts where the amount of 

 lime is quite small, as on some coasts of Europe. Bang (i) has ob- 

 served that the dune sand near the sea contains up to sixteen time- 

 more lime than farther inland. This is a natural result of the wash- 

 ing-out process and decomposition, which takes place on the open 

 sand, and is more effective farther inland, because the supply dimin- 

 ishes with the distance from shore. 



On the upper beach and on the seaward slope of the littoral dune 

 are frequently found fragments of shells that have been carried 

 ashore by the waves. In places where the littoral dune is broken 

 shells are often accumulated in the depressions, while more landward 

 the lime in the animal remains is disintegrated by the carbon diox.d 



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of the rain water. 



