THE BIOLOGICAL CONDITIONS IN THE SOIL 249 



fic ; any plant will be injured by any other within its range, 

 and it may suffer less from one of another kind than from one 

 of its own kind.^ 



Bacterio-toxins. — Several observers, including Greig-Smith 

 (114), Bottomley (42), and others, have claimed to find soluble 

 bacterio-toxins in soils. Hutchinson and Thaysen (140^;, on 

 the other hand, obtained wholly negative results, and con- 

 cluded that soluble bacterio-toxins are not normal constitu- 

 ents of soils, but must represent unusual conditions wherever 

 they occur. But the possibility of the existence of toxins in- 

 soluble in water still remains. 



Normal Conditions on a Heavy Soil. 



Table LXVI. summarises many of the Rothamsted results 

 and shows the conditions normally obtaining on a heavy soil 

 in Hertfordshire under a rainfall of 28-30 inches. 



Table LXVI. — Conditions Normally Obtaining in the Soil at Rothamsted. 



J Thus Burmeister (Fuhl. Landw. Zeit., 1914, 63, 547-556 ; see Rome Bull., 

 X914, 1691) found that couch {Triticum or Agropyron repens) increased the yield of 

 oats, and Dr. Brenchley found that certain weeds had the same effect on the yield 

 of v/heat per plant (New Phytologist, 1917). 



2 Running on occasions up to i*8. ' Occasionally up to 2*3. 



* Occasionally up to 2*5. 



* The concentration of the dissolved matter is of the order of 0*2 per cent, 

 and the osmotic pressure about i atmosphere. 



