492 SCIENCE PROGRESS 



the case. A number of apple trees in a flourishing condition 

 which had been in the ground four years were selected and half 

 of them were grassed over ; the effect produced may be described 

 as instantaneous, for the grassed trees at once ceased to produce 

 any fresh growth and after two or three years the trees of one 

 of the varieties dealt with were all killed. A similar experiment 

 was subsequently made with a mixed plantation {i.e. one con- 

 sisting of standard and dwarf apple, pear and plum trees) which 

 had been established twelve years. The plantation was first 

 divided into halves, so that each half contained a similar col- 

 lection of trees ; on measurement the trees in these two sections 

 were found to be of equal vigour. One section was then laid 

 down to grass. The effect of this treatment was apparent 

 almost at once; and in three or four years the disturbance was 

 so serious that, in the case of some of the varieties, the trees 

 were actually killed ; others remained apparently unaffected 

 for some time but are now falling considerably behind those 

 in the tilled section. 



The only case in which, in our particular soil, the action ot 

 grass seems to be modified is when the grass is allowed to 

 establish itself gradually during the course of several years. 

 The trees under such circumstances appear to adapt themselves 

 to the altering conditions, though even then they do not flourish 

 like those in tilled ground. 



Many of the experiments on grassing trees have been made 

 also in the Harpenden soil ; though the effect produced there 

 is considerably less marked than at the Woburn Fruit Farm, it 

 is still very conspicuous and in some cases the grassing has been 

 fatal. In other localities, the effect of grass may be still less 

 marked but instances of its deleterious action may be observed 

 all over the country and in every class of soil. Only in one 

 instance which has come under our immediate observation has 

 there been no evident action and there seems to be no obvious 

 reason for this failure : it is certainly not because the tree-roots 

 have stretched down beyond the grass-roots, for both sets of 

 roots seem to be intermingled not far below the surface. 



The visible effect of grass is not confined to the arrest 

 of growth ; it is also manifest in the altered colour of the leaves, 

 of the bark and of the fruit. The leaves are much paler than 

 those of healthy trees and assume their autumn tints quite 

 a fortnight before the normal time. The bark also is pale and 



