32 
TENTH REPORT. 
MUTUAL INTERACTIONS OF PLANT ROOTS. 
J. B. Dandeno. 
The idea is not new that plants, in their ordinary activities of life, produce 
upon the soil, through the medium of their roots, an effect which is shown 
frequently in the succeeding crop. This succeeding crop is usually, though 
not always, smaller than the preceding, and smaller than it would be if steps 
be taken to modify the soil in such a way as to counteract this effect. It 
has long been known that roots of plants excrete substances which usually 
react acid. Many plants, of which corn may be taken as a type, give off 
material which is not acid, and it is quite probable that the character of the 
substance liberated, is as diverse as the plants themselves. Up to the present, 
very little is known with respect to such substances, either chemically or 
otherwise, and, in the practice of agriculture, it has never been recognized 
that such substance, if any be excreted at all, could have any bearing upon 
the fertility of the soil. When soil had become poor, the chemist pronounced 
such soil to be lacking in the ordinary inorganic nutritive substances, or 
plant food, as it was called. But when seedlings are used, and distilled 
water as the medium, the matter of external soil food is entirely eliminated, 
and yet, in many respects, results which are similar to those produced in 
soil, are brought about. This subject, of course, is quite closely connected 
with that of the interaction of the roots upon one another, and this is the 
phase of the question, particularly, discussed here. 
The object of the experiments relating to these questions was to gain 
some exact knowledge of the material excreted by roots, and of the inter- 
actions of the roots of one plant upon another. 
After the preliminary experiments and observations had been made, 
two very prominent things began to be apparent. During the first twelve 
to thirty-six hours, certain results developed, which were different from 
those obtained from seedlings grown longer than thirty-six hours. As a 
rule the growth of the radicles of two different seedlings, when grown together, 
was greater than when grown separately for the first eighteen to thirty-six 
hours; after that, the difference was generally the other Way. 
In the case of experiments on growth of radicle .for the first period, the 
difference was generally greatest when in smallest amounts of water; but 
the period of augmented growth was much shortened. In the second period, 
that after thirty-six hours, the results varied, but the quantity of liquid root- 
medium played some part in the results. 
For the first period, the seedlings for the test were taken when the radicles 
had grown about fifteen to twenty mm. long. These seedlings were set 
aside for a period of from sixteen to thirty-six hours and the growth of radicle 
measured. The different species of seeds used, were placed in 25 cc. vials 
in pairs. For example, when seedlings of the species A and B were com- 
pared, 10 pairs of A were put in 10 vials, 10 pairs of B were put in 10 vials, 
and 10 pairs made up of one of A with one of B were similarly placed; and 
in a given time, the total growth of the seedlings A, when grown with 
B was compared with that of A when grown with A. 
As a general rule, the growth of both A and B, when grown together. 
