1909] OLSSON-SEFFER— VEGETATION ON SEA SHORES 105 



The greater or smaller amount of peroxid of iron in dune sand 

 determines to some extent its color. The usually colorless grains of 

 pure quartz are covered with a thin coat of ferric hydroxid, which gives 

 the sand its yellow color, and in some places almost a red tint. 



The soluble salt content in coastal sand. — Of the soluble 

 -alts that saturate the coastal sands sodium chlorid is the most impor- 

 tant. Its presence, as common salt, in all plants is well known, and its 

 influence on the littoral flora is very apparent. Whether sodium chlorid 

 is essential to plant life is still an open question, and the investigations 

 hitherto conducted in order to ascertain this fact seem to indicate that 

 Jch is not the case. In experiments it is difficult to eliminate salt 

 entirely, but it has been conclusively shown that the smallest quan- 

 tities only, if any at all, are needed for the development of plants, even 

 for those which apparently prefer salty situations, when growing under 

 natural conditions. 



That common salt is injurious to plants, when present in excessive 

 quantities, is certain. It is commonly believed that this unfavorable 

 influence of salt is due to the amount of magnesium chlorid it contains, 

 it is more likely, however, that all the chlorids are injurious, and exper- 

 iments by the writer have supported this view, previously maintained 

 °v several authors. 



« is generally stated by various writers that the formations on the 

 * ea coast contain a considerable amn.mf nf mmmnn salt. Thus 



arming (14) sa y S that on the sandy beach the salty ground water is 

 >und at only a slight depth under the surface. Contejean (3), in 

 ^ a 'mg of the conditions in southwestern France, considers that his 



second belt of sea-shore vegetation, that is our middle and upper 



fctth, is growing in a saline soil. 



Masclef 



tent in A ~«mc aun. xvxAaci^r W iuuuu ««. *~~ ~~- 



I- m x S neai " the Sea t0 be 0-35 1 P cr Ccnt -> whUc at a distanCe 



30 from the shore he found 0.17 per cent, of sodium chlorid, and 

 at ] '500- he discovered o . 



041 per cent. 



authoT ChaS bCen S ° me doubt ' however, in the minds of certain 

 or noT VV ?* ether the coas tal dunes are impregnated with common salt 



variou theSe is Massart ( io )- The P resent writer has on 



anal v U ' C ° aStS made tests for salts in the sand h y means of chemical 

 cfrcunJ ThC FCSUlt ° f these observations shows that under ordinar >' 



b a nces dunes do not contain sodium chlorids in perceptible 



