28o DISEASES OF TREES 



the meaning is extended to include innocuous soluble substances 

 which may even be valuable constituents of plant-food when 

 the solutions in which they are present in the soil are in a too 

 concentrated form. The endosmotic process by which the roots 

 take in water can go on only if the cell-sap of the roots is 

 so much more concentrated than the solutions in the soil that 

 it can absorb water rom the environment. On this account 

 any strong solution of food-materials in the soil will prove 

 injurious, and may even attract water from the roots. The 

 result is that the plants wither. Such a state of things may 

 be frequently observed when very soluble mineral manures are 

 applied in excessively large quantities. Other soluble salts which 

 are innocuous in themselves may also cause plants to wither. 



When spring tides have inundated woods situated behind 

 dunes, the water, being unable to return, has slowly percolated 

 into the soil, and the chloride of sodium which sea-water 

 contains has frequently proved extremely injurious. 1 The pine, 

 alder, oak, and beech succumbed altogether and were found to 

 suffer most, while the birch was least affected. In July 1874, 

 along with Herr Schiitze, the chemist at Eberswalde, I insti- 

 tuted investigations on the action of common salt, using solu- 

 tions of the strength of the water of the Baltic (27 per cent.) 

 and of the North Sea (3'47 per cent.) The Scotch pine, spruce, 

 false acacia, and beech were selected for experiment, beds of 

 seedlings and transplanted trees being sprayed with the salt 

 water, each square yard receiving 2-57 gallons at a time. One- 

 and three-year-old spruces succumbed both to the weak and 

 the strong solutions, while six-year-old plants were only killed 

 by the stronger solution, though they became partially brown 

 under the action of the other. When spruces some six feet 

 high each received fully three gallons of the stronger solution, 

 some were killed, while others showed only a temporary brown- 

 ness and ultimately recovered. False acacias one year old were 

 also killed by the weaker solution, while, strange to say, in the 

 case of thirty-year-old beeches it was only the points of the 

 leaves that died, some time after the solution had been applied. 



1 Schiitze, u Untersuchung von Boden und Holz aus Bestanden, welche 

 durch Sturmfluthen der Ostsee beschadigt sind," Zeitschrift fur Forst- 

 und Jagdivesen, 1876, p. 380. 



