THE EFFECT OF GRASS ON TREES 265 



Finally, a plantation of standard Bramley's Seedling apples, 

 which had been established for twenty-three years, and consisted 

 of remarkably vigorous specimens of this variety, was selected, 

 and half of it laid down to grass in 1917. The grass did not 

 come up well, and the hay from it amounted to only three-fifths 

 of a ton to the acre, yet the effect of it on the trees was very 

 apparent, even in that first year. In June the foliage of the 

 grassed section exhibited the light unhealthy tint character- 

 istic of trees suffering from grass, and in the autumn the leaves 

 fell two weeks earlier than those from the trees in the tilled 

 section, whilst the fruit crop was adversely affected to the extent 

 of 5 per cent. In the following season the crop was affected to 

 as much as 89 per cent., and, since the trees were then being 

 evidently ruined by the grass, this latter was removed. 



All these observations justify the conclusion that grass 

 operates prejudicially on fruit trees whatever their age may be. 



That the effect is not confined to apple trees, is shown by two 

 of the three varieties of pear trees mentioned above having been 

 materially affected, whilst several other experiments with pears, 

 plums and cherries, grown both as dwarfs and standards (III, 36), 

 show that the effect of grass on these is similar to its effect on 

 apples. Figs. 33-35 illustrate some of the results obtained. An 

 exact comparison between the magnitude of the grass-effect 

 in the case of these different sorts of trees is hardly possible, 

 but the results of six years' observation may be thus summarised 



Values compared with ungrassed 



trees = 100. 



Leaf -size. Primings. Crops. 



Cherries. 88 * 32 8 



Pears ... 72 21 o 



Plums ... 72 7 i'5 



Apples ... 68 6 



The cherries are probably less affected than the other kinds 

 of trees examined, but these others show no very certain 

 differences as to their susceptibility to grass. The results with 

 apples, however, it should be mentioned, are not quite com- 

 parable with the others, as they apply to values obtained with 

 trees in the ordinary soil of the farm, whereas the other trees 

 mentioned were grown in a raised border with a double depth of 

 soil ; and this, no doubt (see p. 308), reduced the effect of grass 

 on them. 



Subsequent experiments with trees grown in pots indicated 



