SALINE AND ALKAL! LANDS. 533 



explains the discrepancies mentioned, since lime is especially potent in 

 counteracting the injurious effects ; thus throwing additional light upon 

 the importance of the lime-content of alkali soils proper, and also upon 

 the causes of the narrow limitations of the littoral (marine saline) flora ; 

 inasmuch as, unlike alkali soils, marine alluvial lands are by no means 

 always calcareous. Cameron goes so far as to attribute the favorable 

 effects of gypsum upon black alkali not so much to the conversion of 

 the latter into neutral sulfate, as to the effect of gypsum solution in 

 counteracting the saline effects. This interpretation, however, seems 

 rather far-fetched, since there can be no question about the double 

 decomposition of gypsum with carbonate of soda ; or the intense injur- 

 iousness of carbonate of soda in the actual corrosion of vegetable 

 tissues. The corresponding protective influence of various salts, more 

 especially of those of lime, against the injurious effects of pure common 

 salt on marine animals, has already been mentioned (chapter 20, page 

 380), and later investigations by Osterhout on marine algae, show the 

 same relation to hold true for them also. 



Reclamation of Marine Saline Lands for Culture. The 

 reclamation of sea-coast lands and marshes for agricultural 

 use is based in general upon the same methods as those al- 

 ready outlined for alkali lands in chapter 20; except that in 

 this case no chemical neutralization is possible, since common 

 salt cannot be changed by any practically feasible means. It 

 must be removed by leaching, and this, in the humid countries 

 in which such reclamations have chicllv been made, is usually 

 done by the agency of rains, aided by ditching. The 

 " polder " lands thus reclaimed along the shores of the Xorth 

 Sea, from Belgium to Prussia, are especially esteemed for 

 their productiveness, doubtless owing to the alluvium of the 

 numerous rivers tributary to that sea. which is distributed 

 along its shores and in the numerous inlets and bays. The 

 tides are of course excluded by dikes provided with gates 

 opening outward, so as to permit of the outflow of rain- 

 or irrigation-water used for leaching purposes. 



Out of reach of stream alluvium no exceptional fertility is 

 to be expected of sea-shore lands, which then commonly assume 

 the form of sand dunes or bars, incapable of nourishing any 

 cultural vegetation. Of the latter, the groups listed below as 

 tolerant of alkali salts, may also be considered with reference 



