141 



volume of the soil. The plants under experiment stood in glass cylinders 

 of the dimensions and contents given below, received steadily from 30 to 

 60 per cent, of the water required by saturation of the soil and resulted 

 with clover, as follows : 



Diameter in the Clear. 



14 cm. 

 14 cm. 

 14 cm. 

 14 cm. 



Harvested dry substances, 

 in the years 1872, 1873, 1874. 



417.2 g. with 6.92 per cent, pure ash 



254.6 g. " 6.97 " " " " 



173.0 g. " 8.08 " " " " 



76.8 g. " 8.45 " " " " 



Since, in the containers with a very large soil volume, too great a con- 

 solidation, therefore somewhat abnormal conditions for some plants, has 

 appeared, because of the sudden addition at first of great amounts of water 

 saturating the soil to 60 per cent, of its water capacity, Hellriegel, in his 

 harvest tables, explained especially the results for the sizes III and IV. 

 From this it appeared that, with peas, an amount of soil of 



3,100 g. gave on the average, 29.97 in dry substances. 



6,200 g. " " " " 47.94 " " 



For peas, therefore, the proportion of the soil was i :2. 



" " " " " " " harvest was i :i.6. 



For beans, therefore, the proportion of the soil was 1.2. 



" " harvest was i :i.8. 



In 1872, exactly the same proportions in harvest results were found for 

 barley as for beans. We omit here the repetition of the figures, since those 

 cited show clearly enough that, in two equally wide, but unequally tall ves- 

 sels, both containing nutritive substances in excess, and steadily receiving 

 the favorable amount of water, the harvest came out as i :i.6 up to 1.8, if 

 the amounts of soil bore the proportions of i :2. Thus a strikingly evident 

 influence of the soil volume may be confirmed and the question now is, how 

 this influence may be explained. 



Hellriegel found that the height of the yield stood in inverse ratio to the 

 amount of the mechanical resistance, which opposes the development of the 

 root-network of the plants under experiment. 



If commercial growers get apparently opposite results and find that 

 the growth in small pots is great and quick, the explanation lies in the fact 

 that they use a very rich earth and highly concentrated solutions are present 

 in the soil. Comparative measurements showed, however, that the root 

 development in rich nutrient solutions is essentially shorter than in weakly 

 concentrated ones. Hence the demand of the root fibre is actually smaller. 



