372 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
THE ACTION OF ONE CROP ON ANOTHER. 
By Spencer Pickering, F.R.S. 
[Read before the Scientific Committee, Feb. 26, 191 8.] 
The problems connected with the action of one crop on another have 
been engaging our attention at the Woburn Experimental Fruit Farm 
for over twenty years, and it is, naturally, impossible in a short article 
to give more than a very imperfect outline of all the experiments made 
on the subject. 
The work originated in observing the great effect which grass had 
on fruit trees, and the conclusion drawn almost from the outset was 
that this effect must be due to some toxic action. But it will be well, 
in the first instance, to disarm criticism on two points : there can be 
no question but that the extent of the effect of grass on trees varies 
very greatly under different conditions — the nature of the soil, the 
nature of the trees, and probably the meteorological conditions, and 
all the facts which have been ascertained about the action, render 
such variations inevitable : indeed, it is quite possible that in some 
cases the prejudicial action of grass might be nil, though (with the 
exception of a partial instance, to be mentioned below) no such case 
has come under our observation : in various instances where there 
has apparently been no action, the results, on examination, 
have been lacking in some, or all, of the elements of precision which 
would justify conclusions being drawn from them. The second 
point is that toxic action does not necessarily involve the idea of any 
poison] being exuded from the roots : such exudation may occur, 
but there is nothing as yet to prove it ; plant-growth, however, is 
accompanied by the formation of much detritus : this accumulates in 
the soil, being there decomposed by chemical and bacterial agency, 
and eventually, as we know, enriches the soil; but it must pass 
through many phases before this point is reached, and some of the 
intermediate products of its decomposition appear to be harmful to 
vegetation. 
That the baleful effect of grass on trees at our farm is very great, 
there can be no question. Fig. 54 shows results of grass having been 
sown round some standard apples immediately after they had been 
planted, the photograph having been taken three years later : and 
fig. 55 illustrates a similar result with dwarf apples. It was not ex- 
pected that such an effect would be produced on trees after they had 
become well established in the ground, but the effect was, as a matter of 
fact, found to be just as great ; the trees then grassed over had been 
growing for four years in tilled ground, but as soon as the grass grew, 
