THE EFFECT OF GRASS ON TREES 273 



grassed area need be for the trees to show such an effect, for, 

 even after ten years, when the total weights of the trees were one 

 to two hundredweights, the weight of roots within the grassed 

 region was found to amount to only 0*9 to 2*4 ounces per tree. 



Just as a small fraction of the roots of a tree being under grass 

 may cause the appearance of the grass-effect, so the extension of 

 a small fraction of them beyond the grassed area will, in the case 

 of a tree which is under grass, result in some recovery of vigour 

 (III, 9) ; and no recovery has yet been noticed with fruit trees 

 other than that which might be explained in this way. Partial 

 recovery, it is true, has been noticed with other plants suffering 

 from the effect of a surface crop (p. 297), and no doubt may occur 

 with trees, but it is less probable in such a case, for hard-wooded 

 pknts recover only with difficulty from any stunting effect in 

 early life, and even the complete removal of the grass from 

 above their roots, will often not restore them to their natural 

 vigour. 



To what distance it is necessary to remove the grass from a 

 tree when planting it, so as to avoid the grass-effect, must depend 

 on the size of the tree, as well as on many other circumstances; 

 and ho very definite pronouncement on the subject can be made. 

 In one series of experiments at Ridgmont, the vigour of young 

 apple trees, as measured by their leaf-size during four years, 

 and their total weight when subsequently lifted, was 



58, . 62, 74, 89 and 100, 

 when the grass was removed to distances of 



o, 0-5, i, 2 and 20 feet 



from the stems ; showing the existence of some benefit by re- 

 moving the grass even from the six inches of soil around the 

 trees : whilst in another series at Harpenden, where the distances 

 of the grass from the stems were 



o, 2, 4 and 6 feet, 



the increments in the weights of the trees after four years were 

 found to be 



o, 43, 160 and 228 per cent., 



showing an increase in the benefit from the removal of the grass, 

 certainly up to six feet, though, as there were no trees with the 

 grass removed to more than a six feet distance, it was not 

 possible to say whether the limit had even then been reached. 

 T 



