THE BIOLOGICAL CONDITIONS IN THE SOIL 249 



fie ; 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. 1 



Bacterio-toxins. Several observers, including Greig-Smith 

 (i 14), 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. 



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

 1914, 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 wheat per plant (New Phytologist, 1917). 



2 Running on occasions up to 1*8. 3 Occasionally up to 2-3. 



4 Occasionally up to 2*5. 



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

 and the osmotic pressure about i atmosphere. 



