Ill 



These experiments give us some idea as to what percentage of the 

 rainfall remains in the soil for the use of the plant in the case of 

 large and small rains, but do not quite answer the question how one 

 and the same quantity of rain is utilized in moistening the earth 

 when it is distributed through a larger or smaller number of rainy 

 days. 



On this latter question Wollny has made the following experi- 

 ment: A quantity of water corresponding to a rainfall of ()0 milli- 

 meters was communicated to an experimental tub, Xo. 1, all at once, 

 while in tub Xo. 2, 30 millimeters were given the first time and the 

 remaining 30 after three days; in the third tub 20 millimeters were 

 given at first and 20 millimeters every other day thereafter, and, 

 finally, in the fourth tub, 10 millimeters were given every day, so 

 that in six days all had received the same quantity of water. These 

 experiments were repeated for different kinds of soil and the results 

 show that in all cases the quantity of water lost by evaporation is 

 larger the more frequently the water was communicated or the greater 

 the number of rainy days. A fine illustration of the truth of this 

 principle as applied to practice is narrated by Haberlandt, who found 

 that in 1874 the farmers at Postelberg got much better crops than 

 those at Lobositz, which could only be attributed to the fact that 

 during that year Postelberg had received 246 millimeters of rain- 

 fall in forty days, or an average of 6, whereas Lobositz had received 

 309 millimeters in seventy-seven days, an average of 4, so that the 

 usefulness of the gi'eater quantity of rain in Lobositz did not equal 

 that of the smaller quantity at Postelberg. 



Wollnj^ shows that since the period of the heaviest rainfall occurs 

 throughout central Europe at the time of the largest evaporation 

 from the soil we must conclude that for the naked earth the Avetting 

 of the soil during the warmer season of the year is controlled much 

 more largely by the rainfall than by the evaporation depending on 

 the temperature. His observations with the lysimeter show that the 

 precipitation is principally concerned in the moistening of the naked 

 soil during the Avarmer season, while the influence of the temperature 

 and the resulting evaporation nearly disappears and is only observ- 

 able in periods that are deficient in rain. In most cases the vegeta- 

 tion is injured Avhen the atmospheric precipitation during the coldest 

 season of the year is insufficient. The precipitation at this time of 

 the year is therefore quite as important for the success of the harvest 

 as that which falls during the period of vegetation. (WoUny's 

 Forschungen, Vol. XIV, pp. 138-101.) 



A. Seignette has shown that the law of levels propounded by 

 Royer is confirmed. This law states that for given plants and for 

 other uniform conditions the reserve nutriment in the earth is always 

 found at a constant distance below^ the surface; thus the bulbs of 



