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CHAPTER LVII. PSAMMOPHILOUS HALOPHYTES 



THE vegetation on sand is by no means a single formation, but must 

 be divided into several, which are determined by the nature of the soil 

 and particularly by its humidity, and which include various growth-forms. 



If we walk on the shores of northern Europe, say, in Denmark, we 

 meet with the following formations zonally arranged, commencing nearest 

 the sea : 



1. Sand- Algae. 



2. Iron-Sulphur-Bacteria. 



These two occur nearest the sea in the aestuarium. 



3. Halophilous spermophytic herbs. 



4. White dunes (shore dunes) . 



5. Fixed or grey dunes (inland 



dunes). 



6. Sand-fields, in many places. 



These are to be regarded as 

 two formations, and are by no 

 means essentially halophytic. 

 They will be considered in 

 Section X with other psam- 

 mophilous vegetation. 



7. Shingle-banks occasionally. 



8. Halophilous forest and bushland frequently as a succes- 



sion inland. 



a. Sand- Algae. 



These have been already described as part of the microphyte forma- 

 tion of the benthos of loose soil. (See Chapter XLII, p. 175.) 



They also form vegetation beneath spermophytic communities that 

 occur as members of the vegetation succeeding on the landward side. 



6. Iron-Sulphur-Bacteria. 



In the immediate vicinity of the Sand-Algae, but in deeper layers 

 of the shore-soil, there are often black masses of sand, which owe their 

 blackness to the reduction of sulphates dissolved in water contained 

 in ferruginous sand ; in this process, according to Beijerinck 1 and van 

 Delden, 2 definite anaerobic Spirilla (Microspira desulfuricans and others) 

 play an essential part. This formation is not only met with on the 

 sea-shore, but is also general in the mud of fresh-water lakes and pools ; 

 it seethes not only with sulphate-reducing bacteria, but also with Bacillus 

 subtilis and others. 3 



c. Halophilous spermophytic Herbs. 



In this third zone the soil is drier, being flooded with sea-water only 

 occasionally ; the sand is loose and therefore white, dotted with a very open 

 scanty vegetation. One plant stands here, another there, and yet another 

 at a considerable distance an arrangement seemingly due to the very un- 

 settled state of the loose soil, which is disturbed by wind and very high 

 tides. The species are for the most part annual herbs, such as, in North 



1 Beijerinck, 1895. * van Delden, 1903. 



3 Warming and Wesenberg-Lund, 1904; see also Chap. XLII, p. 177. 

 WARMING n 



