TOXIC ACTION OF ONE CROP ON ANOTHER 307 



up to the time when this experiment was discontinued, in the 

 trees showing twice as much vigour as those which had been 

 grassed from the first (XIV, 48). In another case where apple 

 trees, which had been grassed over immediately after being 

 planted, were lifted and weighed at the end of fifteen years, 

 they were found to weigh only one-third as much as similar 

 trees where the grassing had been allowed to occur gradually 

 (XIII, 25). 



These results enable us to deal with an objection which is 

 always raised when the Woburn results on the grassing of trees 

 come under discussion, namely, How can such results tally 

 with the flourishing condition of fruit trees under grass in other 

 parts of the country? The flourishing condition of such trees, 

 however, may require some qualification : they may not be 

 affected to the same extent as those in most of the Woburn 

 experiments, but, in the almost invariable absence of definite 

 measurements, and of the means of comparing them strictly with 

 similar trees in tilled ground, it is impossible to state that they 

 have not suffered at all from the grass. In every case where strict 

 comparisons have been made, such an effect is noticeable, and 

 may be of considerable magnitude, even where to all appearance 

 the trees are flourishing satisfactorily. An instructive instance 

 in point is afforded by the experiments at the National Fruit 

 and Cider Institute, Long Ashton : 1 eight varieties of standard 

 apples were planted in grassed land, and in some cases the 

 grass was allowed to re-establish itself round the stems, whereas 

 in other cases, spaces measuring about nine feet in diameter 

 were kept tilled. After three and five years the differences in 

 girth of stems of the two sets of trees were only 17 and 13 per 

 cent., and any one examining the grassed trees would have 

 pronounced them as being in a flourishing condition. But 

 differences in girth and in the weight of the trees would be in 

 the proportion of a square to a cube, so that the deficiency in 

 weight of the grassed trees would be 22 per cent., and, on the 

 conservative assumption that the trees had not more than 

 doubled their weight since being planted, this would mean that 

 the increase in weight of the grassed trees had only been half 

 that of the trees in the tilled ground. In another case where 

 similar experiments were made in Gloucestershire under the 

 auspices of the Fruit and Cider Institute, 2 differences in girth 



1 Nat. Fruit and Cider Inst. Rpts., 1908, 1909, 1911. Also Jour. Bath 

 and West Soc., Series V, 1910-11 ; VIII, 140. 



2 Pamphlet of the Gloucestershire Education Committee, by G, H. 

 Hollingworth, Oct. 1913. 



