280 SCIENCE AND FRUIT GROWING 



much as 92 per cent. (XIII, 96). The average values for the 

 three years were 



No alkali .... Vigour = 100 

 Quarter dose alkali . . ,, 99 



Half dose alkali ... ,, 89 



Full dose alkali . 81 



Grass ....,, 47 



The physical condition of soil under grass and under tillage 

 was then examined. Five pairs of stations : with tilled and 

 grassed ground, immediately adjoining each other, were selected 

 at Ridgmont, two similar pairs at Harpenden, and one pair at 

 Millbrook ; these were sampled to three successive depths of 

 six inches each, and the samples shaken with water. In one 

 case the liquids were allowed thirty minutes for settlement, 

 and then the supernatant liquid drawn off, which would contain 

 in suspension the finest, and also the moderately fine matter; 

 in another case the liquid was left for eighteen hours before 

 being decanted, and this, of course, would contain only the 

 finest particles. Taking the three depths of six inches together, 

 there was practically no difference between the proportions of 

 fine matter in the tilled and grassed soils : the averages, when 

 thirty minutes were allowed for settlement, were 1-677 and 1-662 

 grams, respectively, per 100 grams of soil taken, and when 

 eighteen hours were allowed, the percentages were 0-332 and 

 0*313, respectively. 



Nor did there appear to be any radical difference in the 

 distribution of the fine particles throughout the eighteen inches. 

 This may be best seen from the accompanying illustrations. 

 In Fig. 37, A, the line T represents the distribution of the 

 fine particles in the tilled soil, and the line G that in the 

 grassed soil; they are almost identical, showing that, though 

 the proportion of fine particles increases considerably as greater 

 depths are reached, it does so at almost the same rate at a 

 very slightly diminishing rate in the case of the tilled soil, and 

 at a practically constant rate in the case of the grassed soil. 

 When the values for the finest particles are similarly set out 

 (Fig. 37, B) the results bear a very different aspect, there being 

 a great accumulation of these finest particles at about nine 

 inches below the surface, but the accumulation is, again, prac- 

 tically the same for the tilled and grassed soils, the figures repre- 

 senting the results being almost coincident. Hence there are 

 no differences in the distribution of soil particles such as could 



