94 BOTANICAL GAZETTE [February 



absorption by the plant of saline water has been discussed consider- 

 ably, and several theories have been advanced. 



Precipitation is a factor, which on naturally dry soil, such as pre- 

 sented by sand formations, is of considerable importance, not only on 

 account of the quantity of water which in this way is brought to the 

 plants, but also because of its influence in giving coherence to the sand, 

 thus preventing it from shifting, and because of its weathering action 



on the soil particles. 



That precipitation must to a great extent influence the develop- 

 ment of vegetation on marine coasts is evident, and it is easily seen 

 that the composition of the plant covering of sand formations vanes 

 somewhat in rainy and rainless climates, although the atmosphenc 

 humidity on the coast tends to minimize this difference. The latter 

 factor is especially important as the precipitation often is so variable. 

 The absolute amount of rain during the year does not in fact give am 

 correct basis for comparison of the conditions in different localities, 

 as it is far more important for the vegetation how this quantity B 

 distributed over the period in question. On the Baltic shores the 

 number of rainy days of the vegetative season is much greater than. 

 for instance, on the coast of Australia or California. The eastern 

 coast of Australia, at Brisbane, has an average yearly rainfall ot 

 129. 5 cm while the Aland Islands in the Baltic have only 52.9 cn \ but 

 the vegetation in the latter region has a much more even supply ot 

 moisture during the vegetative season, because the precipitation 1 

 distributed over a greater number of days, about 70 of the 160 rain} 

 days of the year falling in the growing season. 



Edaphic factors 



"«vu .v^^, pvpvEKu tin:* tcini v*°y8) he apparently regarded 

 it as covering all the peculiarities of the ground. It seems to the 

 present writer that it would be more convenient in this connection to 

 distinguish between the soil as such, and the media, water and air, 

 tilling the interstitial spaces. This distinction has been made in tbis 



moisture 



hydrodynamic, and the factors pertaining to the soil proper as edaph 



ery greatest 



admitted to be 01 v* 



, . ,. . -1— ^~« 1 



