EXPERIMENTS IN MANURING IN POTS AND IN THE FIELD. 121 



to the plant only a certain percentage of their water, 

 basing his opinion on the observation that the plant wilted 

 while the soil still contained a good deal of moisture, in 

 some cases as much as 12°/°. It was also found, by calcu- 

 lation, that the wilting took place in all soils when the 

 film of hygroscopic moisture had diminished to a certain 

 thickness, viz., about '00003 inch. Now it has been proved 

 by numerous investigations beyond all reasonable doubt, 

 notwithstanding the opinion expressed by Prof. Whitney, of 

 the United States Soil Bureau, in recent papers to the 

 contrary, that the concentration of the soil moisture is as 

 a general rule much greater in clay soils than in sandy 

 ones, and it is just in these clay soils that Sachs found the 

 disposition to wilt with the greatest amount of moisture, 

 whereas in sands the plants (tobacco in this instance) 

 remained turgid while only l-§-°/> of water remained. Is it 

 not possible that the retarded development and wilting 

 were due to the too great concentration of the salts, 

 manurial and otherwise, in the soil moisture ? Again, a 

 good deal of irregularity is noticeable in the results obtained 

 in various parts of the world as to the tolerance of certain 

 crops to injurious salts, such as common salt and carbonate 

 of soda. 



It seems to me that the quantity of moisture present in 

 the soil is one of the most important considerations in such 

 experiments, as for instance, a plant would grow as well 

 in a soil, ceteris paribus, containing 4°/° of salt and 40°/° of 

 moisture, as in one containing l°/» of salt and 10°/° of water. 

 This is a question of great importance in some countries, 

 notably our own, and it may not be out of place to suggest 

 that perhaps if maximum and minimum moisture contents 

 of the soils experimented on were determined, much light 

 would be thrown on the apparent discordance of results 

 obtained in different countries. 



