225 



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. 



White dunes (shore dunes). \ J^'^'f ^^%.^^ ^^ '^^^'^l^ ^^ 

 ^ ' two formations, and are by no 



4 



5. Fixed or grey dunes (inland I means essentially halophytic. 



They will be considered in 

 Section X with other psam- 

 mophilous vegetation. 



dunes). 



6. Sand-fields, in many places. 



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 

 ( iccur as members of the vegetation succeeding on the landward side. 



b. 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 ^ and van 

 I3elden,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 

 subtihs and others.^ 



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 



Beijerinck, 1895. * van Delden. 1903. 



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



WARMING Q 



