326 SCIENCE AND FRUIT GROWING 



result of this is that the state of flocculation of a clay soil must 

 vary with the amount of washing to which it has been subjected 

 by the rain. Variation from this cause was found to be very 

 considerable. 



A small patch of ground was marked off at Ridgmont, and 

 samples were drawn from it every month throughout 14 months, 

 in order to determine the state of flocculation of the clay in 

 it (XIV, 37). Three samples were taken on each occasion and 

 mixed together, but those from the first, second and third depths 

 of six inches each, were examined separately. Each sample was 

 shaken up with ten times its weight of water for 24 hours, and, 

 after allowing four hours for subsidence, the upper half of it was 

 syphoned off, and the fine matter still suspended in it, determined. 

 The percentage proportion which this fine matter bore to the 

 weight of soil taken when the whole 18 inches depth of soil was 

 considered, is depicted in the upper diagram in Fig. 46. The 

 variation from month to month was considerable from o'2 to 

 0'5 per cent. but did not show consistently any definite connec- 

 tion with the season of the year. If, however, the rainfall for the 

 20 days preceding the sampling be plotted out, as has been done 

 in the middle diagram, a connection of a very intimate character 

 between these two phenomena is observed : in every case, the 

 higher the rainfall has been, the greater is the proportion of fine 

 particles in the soil, the rain having deprived the clay particles 

 of compounds united to them, and thereby caused their de floccula- 

 tion. It was found, moreover, that the distribution of the fine 

 particles throughout the 18 inches of soil was altered in a similar 

 manner, the relative proportion in the upper 6 inches being greater 

 or less, according as the preceding rainfall had been greater or 

 less : so that not only does the rainfall increase the total amount 

 of fine particles present, but it affects in this respect the surface 

 soil much more than the subsoil. The relative proportion of 

 fine particles in the upper 6 inches as compared with that in the 

 total 18 inches is shown in the lower diagram of the figure. The 

 effect of rain in making a clay soil less workable is thus explained. 



Of course if the rainfall during a much longer period were 

 considered, no connection of the above description would be 

 likely to be traceable, the effect of any given fall having become 

 obliterated by subsequent meteorological conditions : similarly, 

 if the period were too short, the changes wrought by the rain 

 would not have had time to become complete. It was found that 

 if periods of 30 days, on the one hand, or of 10 days, on the other, 

 were taken, the connection between rainfall and the condition of 



