308 SCIENCE AND FRUIT GROWING 



measurement of 33, instead of 15, per cent, were obtained : 1 

 and in all these cases, it may be remarked, the grass cannot 

 have exerted its greatest possible effect, for the grassing of the trees 

 was allowed to occur gradually : added to which, with the trees 

 under tillage, the open spaces round them were not large enough 

 to prevent some of the roots from penetrating into the grassed 

 area before the expiry of the four years, so that they did not 

 form an adequate standard with which the grassed trees could 

 be compared. 



In ordinary practice the grassing of trees is allowed to take 

 place gradually, thus reducing the effect of the grass as indi- 

 cated, but probably the most potent factors in rendering this effect 

 less than at Ridgmont are generally the greater depth of soil 

 available, and a more efficient drainage. The good soil at the 

 Fruit Farm is not more than six or seven inches in depth, and 

 telow it there is a stiff clay subsoil into which roots will not 

 readily penetrate, and which must retard the removal of toxic 

 products : even in the case of stocks which are naturally deep- 

 rooting, the roots spread themselves out near the surface as if 

 they were of a shallow-rooting habit : the illustrations in Fig. 44 

 will afford sufficient evidence of this. But, as has been seen from 

 the experiments quoted on p. 306, the deleterious action of 

 grass is not felt, and may even be changed into a beneficial 

 action, when the tree-roots are separated (in an horizontal direc- 

 tion) by only a few inches of soil from the grass-roots, and in 

 the case of a deep, fertile soil, where the tree-roots find no 

 difficulty in penetrating downwards, they may well get away 

 from the grass-roots sufficiently to materially reduce the deleteri- 

 ous effect of the latter on them. The soil at Long Ashton, is of 

 exceptional depth and fertility. 



The effect of* good drainage is probably still more potent in 

 reducing the toxic action of the grass : a striking illustration 

 of this has been afforded (p. 298) by the growth of plants in 

 trays under conditions where drainage occurred, and where it 

 did not : a similar difference of effect would exist in the 

 case of trees under the toxic action of grass. It is noticeable 

 that the effect of grass on trees is often very small in light and 

 well-drained soils, whilst at Ridgmont, where the effect is very 

 great, the drainage of the soil is particularly bad. Even at 

 Ridgmont itself there is a striking illustration of the importance 

 of drainage, for there are in the farm two similar plantations 



1 Similar experiments at the Harper- Adams College (Joint Report, 1912) 

 gave differences of 25 per cent, after one year, and 45 per cent, after 5 years. 



