OF SAND FOBMATIONS ON MABINE COASTS. 35 



The nutritive value of the sand is very different according to the 

 chemical character of the grains. The commonest form, or quartz sand, 

 is the most barren on account of the insolubility of the quartz grains, and 

 also because of their resistance to decomposing agencies, as already men- 

 tioned. S'and consisting of mica, felspar, limestone, and other minerals, 

 disintegrate, however, and have by reason of this a higher nutritive 

 value. 



Formation of mould takes place only to a small degree in dry sandy 

 soil, because the organic constituents are so easily decomposed through 

 the admittance of air, and the particles are further quickly distributed 

 and carried out of reach of the plants by sinking with the water through 

 the loose soil. The proportion between organic and inorganic constitu- 

 ents in this soil is too great, the quantity of the former being too small 

 to establish a sufficient supply for the demand of a more luxuriant growth 

 of plants. 



This scarcity of plant food results in a more or less open vegetation 

 consisting of low growing plants, which do not give each other the mut- 

 ual assistance against mechanical influence of wind and other factors, 

 that is evident in the arrangement of plants on most other soils. The 

 injurious effect of the intense light, both direct and reflected from the 

 surface of the sand, has to be guarded against. The transpiration of 

 open sand vegetation, especially on the seacoasts, is always considerable 

 because of the constantly changing atmosphere, resulting from the almost 

 continuous winds. The plants have to develop some means of reducing 

 this excessive transpiration. 



Summing up, we may say that the competition for food is more in- 

 tense, the water supply less, the light stronger, the temperature higher, 

 the transpiration greater, the foothold more uncertain and difficult, the 

 conditions for plant life generally more adverse, than on any other soil. 



