270 SCIENCE AND FRUIT GROWING 



reduced by the grass from 100 down to 43, 19 and I, respectively, 

 according as the grass was shallow-rooting, intermediate or deep- 

 rooting. Clover exercised about the same effect as shallow- 

 rooting grasses, and the only peculiarity in its action con- 

 sisted in its not affecting the colour of the leaves of the trees 

 (XIII, 45). 



Then came, the question as to the influence of the nature of 

 the soil on the action of grass. As a result of general observa- 

 tion it is fairly evident that the action varies very greatly in 

 different localities, but whether that is due to differences in the 

 nature of the soil, differences in the depth of soil, or to other 

 differences, is not so clear. Many of the experiments on grassing 

 trees were made at Harpenden, where the soil is considerably 

 deeper than at Ridgmont, less retentive of water, and overlies 

 a different geological formation. The results obtained there 

 showed considerable divergence : in one case the planting of 

 trees in old meadow pasture, with the turf replaced over the 

 roots, resulted in the death of the trees (III, 20), and the grassing- 

 over of a section of a twelve-years-old orchard effected a reduction 

 in vigour equal to that observed in a similar case at Ridgmont, 

 the leaf-size being reduced in five years to 73 and 76 per cent, 

 in the two cases (III, 20) : but, on the other hand, in two 

 other situations at Harpenden the gradual grassing over of 

 established trees produced but little visible effect in one case, 

 and none at all in the other, though actual measurements, and 

 a comparison with check plantations in tilled ground, were not 

 available (XIII, 24). 



The Fruit and Cider Institute at Long Ashton is one of the 

 few places where definite observations on the effect of grass 

 on fruit trees have been made, and there can be no doubt but 

 that the effect there is considerably less than it is at Ridgmont, 

 as some of the results, quoted on p. 307, will show. The relative 

 action of grass on trees in the Ridgmont and Long Ashton 

 soils was, therefore, examined, under such conditions that 

 all factors were eliminated except the nature of the soil itself, 

 the experiments being conducted in pots ; at the same time a 

 light sandy soil from the Stackyard Field at the Royal Agricul- 

 tural Society's farm was similarly examined, as well as pure 

 sand with the requisite nutrients added to it. Instead of grow- 

 ing apple trees in the pots, tobacco plants were grown, with 

 (or without) a surface crop of grass, the arrangement being one 

 which will be described later on (p 291). The general results were 



