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partially unfit for the succeeding crop of the same kind. Different 
crops growing in the same soil may injure each other, or the one the 
other. Two theories are advanced to explain these antagonisms of 
plants. One is that plants excrete toxins; the other is that the 
injurious effect is the result of bacterial activity. 
Mr. Spencer Pickering, of the Woburn Experimental Fruit Farm, 
in accounting for the injurious effect of grass upon young Apple 
trees, attributes the harm done neither to competition between grass 
and tree for moisture and food, nor to a difference in temperature. He 
holds that it is due, not to excessive amounts of carbonic acid, but to 
some “ actively malignant ” effect on the trees, some action on them 
akin to direct poisoning. More recently, Mr. Pickering leaves the 
question open as to whether the harmful action is the effect of a 
poison (toxin) excreted by the roots of the grass, or whether it is the 
result of some change in the activity or composition of the micro-flora 
brought about by the grass sod. Beside these specific experiments 
with Apple trees and grass there have been recently several investi- 
gations with other plants to show that vegetable organisms have 
interdependences other than those with their physical environment. 
For example, investigations with Peach trees grown in pots with 
several plants show that the Peach does not thrive if its roots are in 
close proximity to those of certain other plants. 
The well-being of nearly all plants which minister to the needs 
of man is improved by tillage. Fruit trees not only respond to high 
cultivation in the nursery row, but they need good treatment after 
transplantation to the orchard. 
In experiments to determine what are the comparative effects of 
tillage and grass sod on the Apple tree, it is found that tillage is 
generally better than sod, but it should not be expected, however, 
that sod will be deleterious in the same degree under all conditions. 
It is reasonable to suppose, for instance, that in a deep soil, 
where the Apple tree roots can escape from the grass roots, or in one 
containing a great amount of soil moisture, the harmful effects of the 
grass will not be so marked as in cases of an opposite nature. 
Investigations do not show that the Apples cannot be grown in sod. 
There are many orchards which prove the contrary. It is suggested, 
however, the Apples thrive in sod, not because of the sod, but in 
spite of it. The proof that there are many thrifty orchards in grass 
sod is not proof that these orchards would not do better under tillage. 
The statement is often made that trees will become adapted to 
grass. There is nothing in the experiments conducted in this country 
or in the Colonies to indicate that such is the case. Trees planted 
in sod begin to show ill-effects even in the first year in which orchards 
are laid down to grass, and each succeeding year but adds to the 
injury. Trees can hardly be expected to become adapted to thirst, 
starvation, asphyxiation and poisonous excretions. 
J. J. Willis Harpenden. 
(The Gardeners' Chronicle, November 20, 1909. p. 337.) 
