122 



Hellriegel's experiments gave 80 to 60 and sometimes 40 per cent, 

 Fittbogen's gave 40 to 30 per cent, Wollny's gave 80 to 60 per cent 

 of moisture for the maximum harvest. These differences undoubt- 

 edly arose, at least in part, from differences in richness of the soil, 

 the closeness of the plants, and differences in the sunshine and wind. 

 These results are therefore in general only relative, and justify us 

 in saying that the best crops are obtainable when the earth contains 

 from 40 to 80 per cent of its maximum capacity for water and that 

 the percentage is higher in proportion as the soil is richer; as the 

 plants are closer; as the leaves of the plants are broader; as the 

 sunshine, the dryness of the air, and the velocity of the wind are 

 greater ; and as the barometric pressure is less, since all these increase 

 the useful evaporation from the leaves and the wasteful evaporation 

 from the soil. 



The growth of the auxiliary organs was shown by Fittbogen, who 

 gives the weight of the organic matter as determined by burning the 

 Avell-washed roots, and is also shown by Haberlandt by the weights 

 oi the roots and stubble. Their measures are given in the following 

 tables : 



FITTBOGEN'S EXPERIMENTS. 



HABERLANDT'S EXPERIMENTS. 



