Mixncliestcr MeiHoirs, Vol. Iviii. (1914), No. i\. 13 



washed out of the sand, etc. (see photograph PL V.), 

 showed that they had been able to develop freely in the 

 coarse sand and kaolin but had been greatly restricted in 

 the fine sand and silt. Comparative water cultures were 

 then arranged, in which one series were not aerated at all, 

 whereas in the other bottles a continuous current of air 

 was bubbled through the solutions. The experiment was 

 repeated with barley and lupins, and the results obtained 

 are sufficiently seen from the photograph, P/. VI., of a 

 typical pair of aerated and non-aerated cultures. 



These results are convincing as to the enormous gain 

 to the plant from continuous aeration of the root, and to 

 this factor alone may be set down the superiority of the 

 cultures in solid media over the ordinary water cultures 

 in which the aeration is not continuous. 



Though several minor points remained for considera- 

 tion they need not be here discussed, as they did not in 

 any way modify the main results already set out. 



The conclusions can only be regarded as entirely 

 adverse to the theory of Whitney and Cameron. That 

 begins by postulating a soil solution of constant com- 

 position in saturated equilibrium with the phosphates and 

 potash compounds which, though varying in amount, 

 should be practically identical in all soils. The solutions 

 from the Rothamsted soils were, however, found to 

 vary in composition in accord with their past manurial 

 history. Thus we must conclude that the compounds 

 of phosphoric acid and potash in the soil are by no 

 means .so simple and definite as they had been 

 supposed, but vary within wide limits in their solu- 

 bility according to their origin and the nature of 

 the general mass of soil particles. Furthermore, 

 the growth of the plant varied directly, though not 

 proportionally, with the concentration (within wide limits) 



